Legion III. NASSELLARIA, (continued 3)

The Trissocyclida represent the fourth and last subfamily of Coronida, distinguished from all others in the possession of three complete rings, perpendicular one to another, and of eight large gates separated by them. Two of the three rings are vertical (the primary sagittal and the secondary frontal ring), the third is horizontal (the basal ring). The four upper gates correspond to the four lateral gates of the preceding three subfamilies; the four lower gates are the same as the four basal gates of Semantrum (two primary jugular and two secondary cardinal gates); therefore the Trissocyclida may be derived directly from these Semantida by development of a complete frontal ring. Probably the two jugular gates were originally smaller than the two cardinal, but usually they have become equal. In Tristephanium (the common ancestral form of the Trissocyclida) and in the closely allied Tricyclidium the four basal gates remain smaller than the four lateral gates. But in two other genera, Trissocircus and Trissocyclus, the four lower or basal gates reach the same size as the four upper or lateral gates; therefore all eight gates become equal and the basal ring becomes equatorial. In the most regular species of the latter genera also the three rings become perfectly equal and cannot be any longer distinguished. Here the original bilateral (or dipleuric) fundamental form of the shell passes over into a regular cubic or octahedral form (with three equal, isopolar axes, perpendicular one to another). The eight large gates of the Trissocyclida usually remain simple (Tristephanium, Trissocircus), but sometimes they become partly closed by loose lattice-work (Tricyclidium, Trissocyclus).

The original rings, and the secondary rods or bars, composing the loose framework of the Coronida are either roundish (with circular or elliptical transverse section) or three-edged (with triangular transverse section), rarely quadrangular or provided with distorted edges. The branches or spines arising from them, are either simple or branched, and offer a great variety in number, form, and disposition. The most important forms are those which develop the three typical basal feet of Cortina, e.g., Podocoronis cortina (Pl. 97, fig. 2).

The Central Capsule of the Coronida is the same as in the other Stephoidea (comp. p. 937), and offers all those characteristic peculiarities of "Monopylea" which we have mentioned above in the general description of the Nassellaria (p. 890). Usually it is spherical or ellipsoidal, often violin-shaped or bilobed, with a sagittal constriction. The porochora of its basal pole is in close contact with the base of the sagittal ring.

Synopsis of the Genera of Coronida.

I. Subfamily Zygostephanida. Four lateral gates (no basal gate). Two meridional rings (sagittal and frontal) complete, perpendicular to one another (no basal ring). Four lateral gates simple, 414. Zygostephanus.

Four lateral gates partly latticed, 415. Zygostephanium.

II. Subfamily Acanthodesmida. Five large gates (four lateral and one simple basal). Two meridional rings (sagittal and frontal) incomplete, both truncated by the complete horizontal basal ring. Four lateral gates simple, 416. Coronidium.

Four lateral gates partly latticed, 417. Acanthodesmia.

III. Subfamily Eucoronida. Six large gates (four lateral and two basal). Two rings (the sagittal meridional ring and the horizontal basal ring) complete, the frontal meridian ring incomplete. Basal ring without larger descending feet. Gates simple, 418. Eucoronis.

Gates partly latticed, 419. Plectocoronis.

Basal ring with large, regularly disposed, descending feet. Gates simple, 420. Podocoronis.

IV. Subfamily Trissocyclida. Eight large gates (four upper lateral and four lower basal). Two meridional rings (sagittal and frontal) and the horizontal basal ring complete. All three complete rings perpendicular to one another. Four upper gates larger than the four lower. Gates simple, 421. Tristephanium.

Gates partly latticed, 422. Tricyclidium.

All eight gates of equal size. Gates simple, 423. Trissocircus.

Gates partly latticed, 424. Trissocyclus.

I. Subfamily Zygostephanida. Four lateral gates (no basal gate).

Two meridional rings (sagittal and frontal) complete, perpendicular to one another (no basal ring).

Four lateral gates simple,

414. Zygostephanus.

Four lateral gates partly latticed,

415. Zygostephanium.

II. Subfamily Acanthodesmida. Five large gates (four lateral and one simple basal).

Two meridional rings (sagittal and frontal) incomplete, both truncated by the complete horizontal basal ring.

Four lateral gates simple,

416. Coronidium.

Four lateral gates partly latticed,

417. Acanthodesmia.

III. Subfamily Eucoronida. Six large gates (four lateral and two basal).

Two rings (the sagittal meridional ring and the horizontal basal ring) complete, the frontal meridian ring incomplete.

Basal ring without larger descending feet.

Gates simple,

418. Eucoronis.

Gates partly latticed,

419. Plectocoronis.

Basal ring with large, regularly disposed, descending feet. Gates simple,

420. Podocoronis.

IV. Subfamily Trissocyclida. Eight large gates (four upper lateral and four lower basal).

Two meridional rings (sagittal and frontal) and the horizontal basal ring complete. All three complete rings perpendicular to one another.

Four upper gates larger than the four lower.

Gates simple,

421. Tristephanium.

Gates partly latticed,

422. Tricyclidium.

All eight gates of equal size.

Gates simple,

423. Trissocircus.

Gates partly latticed,

424. Trissocyclus.

Subfamily 1. Zygostephanida, Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with four large lateral gates, without basal gate. Skeleton composed of two complete vertical rings, perpendicular one to another—the primary sagittal and the secondary frontal ring.

Genus 414. Zygostephanus,^[33] Haeckel, 1862, Monogr. d. Radiol., p. 268.

Definition.—Coronida with four large, simple, lateral gates, without basal gate and lattice-work. Skeleton composed of two simple meridional rings, perpendicular to one another.

The genus Zygostephanus, founded by me in 1862 for the Mediterranean Zygostephanus mülleri, is the simplest and most primitive of all the Coronida, and may therefore be regarded as the common ancestral form of this family. The simple skeleton is composed of two meridional rings only, perpendicular one to another—a sagittal and a frontal ring.

Subgenus 1. Zygostephus, Haeckel, 1881, Prodromus, p. 446.

Definition.—The two vertical rings of nearly equal height, therefore without sagittal constriction.

1. Zygostephanus dissocircus, n. sp. (Pl. 93, fig. 1).

Both rings elliptical, of nearly equal height, smooth, without spines. Frontal ring somewhat longer than the sagittal. No sagittal constriction.

Dimensions.—Height of the rings 0.07, breadth 0.1.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

2. Zygostephanus serratus, n. sp.

Both rings elliptical, of nearly equal height, with a serrate prominent edge on the outer convexity (in the transverse section three-edged). No sagittal constriction.

Dimensions.—Height of the rings 0.08, breadth 0.12.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

3. Zygostephanus mülleri, Haeckel.

Zygostephanus mülleri, Haeckel, 1862, Monogr. d. Radiol., p. 268, Taf. xii. fig. 2.

Both rings elliptical, of nearly equal height, armed with numerous (about fifty) slender curved spines, as long as the radius of the rings; commonly each ring with twelve pairs of divergent spines. No sagittal constriction.

Dimensions.—Height of the rings 0.06, breadth 0.1.

Habitat.—Mediterranean (Messina), surface.

4. Zygostephanus ramosus, n. sp.

Both rings elliptical, of nearly equal height, armed with numerous branched spines, which are arranged on each ring in two divergent rows; the branches of the spines are curved and partly protect the open gates. No sagittal constriction.

Dimensions.—Height of the rings 0.07, breadth 0.09.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

Subgenus 2. Zygostephaniscus, Haeckel, 1881, Prodromus, p. 446.

Definition.—The two vertical rings of different heights; the frontal ring higher than the sagittal ring, therefore with a sagittal constriction in the median plane.

5. Zygostephanus reniformis, n. sp.

Frontal ring kidney-shaped, in the upper half convex, in the lower concave, in the latter with a deep sagittal constriction, armed with numerous irregular short spines. Sagittal ring thicker and lower, only two-thirds as high, with four pairs of short divergent spines (two ventral and two dorsal pairs).

Dimensions.—Height of the frontal ring 0.13, breadth 0.2.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

6. Zygostephanus violina, n. sp.

Frontal ring violin-shaped, on the upper and the lower margin concave, with a deep sagittal constriction, armed with numerous irregular spines, which are partly simple, partly branched. Sagittal ring thicker and lower, only half as high, with a few short conical spines at the apical and basal poles.

Dimensions.—Height of the frontal ring 0.12, breadth 0.18.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

7. Zygostephanus bicornis, n. sp. (Pl. 93, fig. 2).

Frontal ring violin-shaped, on the upper and the lower margin concave, with a deep sagittal constriction; its two halves pentagonal. Between numerous smaller spines there arise from the frontal ring six groups of larger branched spines, two odd in the corners of the highest points (curved like two horns), two branched pairs on the prominent lateral corners (at right and left), and two pairs in the corners of the lowest points (like four branched basal feet). Sagittal ring only two-thirds as high, with four pairs of irregular spines.

Dimensions.—Height of the frontal ring 0.11, breadth 0.16.

Habitat.—South Pacific Station 300, depth 1375 fathoms.

Genus 415. Zygostephanium,^[34] Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with four large, partly latticed, lateral gates, without basal gate. Skeleton composed of two meridional rings perpendicular to each other.

The genus Zygostephanium differs from the preceding ancestral genus Zygostephanus in the development of lattice-work along the two crossed rings, produced by their anastomosing branches. Therefore the four large lateral gates between them, which are quite simple, in the preceding genus here become more or less fenestrated.

1. Zygostephanium dizonium, n. sp. (Pl. 93, fig. 3).

Tympaniscus dizonius, Haeckel, 1882, Manuscript.

Both rings elliptical, of nearly equal height, smooth, without spines. Sagittal ring with four pairs of small pores (two apical pairs and two basal pairs). Frontal ring with three pairs of small pores (one pair lateral, one pair above and one pair below).

Dimensions.—Height of the frontal ring 0.08, breadth 0.12.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

2. Zygostephanium paradictyum, n. sp. (Pl. 93, fig. 4).

Frontal ring kidney-shaped, in the upper half convex, in the lower concave, in the latter with a deep sagittal constriction. Sagittal ring ovate, about two-thirds as high as the frontal ring. Both rings three-edged, armed with numerous short and branched bristle-shaped spines, which anastomose along their three edges and produce two series of irregular polygonal pores.

Dimensions.—Height of the frontal ring 0.08, breadth 0.13.

Habitat.—North Pacific, Station 236, surface.

3. Zygostephanium constrictum, n. sp.

Frontal ring violin-shaped, concave on the upper and lower margins, with a deep sagittal constriction. Sagittal ring ovate, about two-thirds as high as the frontal ring. Both rings covered with numerous branched irregular spines, which partly anastomose along the edges of the rings, and produce small irregular polygonal pores.

Dimensions.—Height of the frontal ring 0.12, breadth 0.18.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

Subfamily 2. Acanthodesmida, Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with five large gates (four lateral and one basal). Skeleton composed of three rings, perpendicular one to another, two of which are vertical and incomplete (the primary or lateral, and the secondary or frontal), the third is horizontal and complete (the tertiary or basal ring).

Genus 416. Coronidium,^[35] Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with five large simple gates (four lateral and one basal). Skeleton composed of two incomplete meridional rings and one complete basal ring, without lattice-work.

The genus Coronidium and the following, nearly allied Acanthodesmia, form together the peculiar subfamily of Acanthodesmida—not in the wider sense in which I first founded this group (1862, Monogr. d. Radiol., p. 265), but in the restricted sense, which is exactly defined in my Prodromus (1881, p. 445). According to this definition, the shell is composed of three different rings, perpendicular to one another; only one of these is complete, the simple horizontal basal ring; the two others are incomplete and vertical (the primary or sagittal and the secondary or frontal ring). Therefore there remain constantly between the three rings five characteristic large openings or gates; four of these are lateral (between the halves of the two meridional rings), the fifth is basal, enclosed by the horizontal basal ring. The longest known type of this subfamily is Acanthodesmia vinculata, the five characteristic gates of which are clearly distinguished by its discoverer, Johannes Müller ("Das Gehäuse besteht nur aus den Leisten zwischen fünf grossen Lücken"). The Acanthodesmida may be derived from the Eucoronida by reduction of the basilar rod of the sagittal ring. If in Eucoronis this basal rod be lost, Coronidium arises.

1. Coronidium dyostephanus, n. sp. (Pl. 82, fig. 7).

Frontal ring elliptical, with few scattered thorns, twice as broad as high, and three times as broad as the smooth rhombic basal ring. Sagittal ring semicircular, very stout, twice as thick as the two other rings, with short lateral thorns (in the figure seen from the apical pole, which exhibits a four-lobed dimple). Basal gate rhombic.

Dimensions.—Height of the frontal ring 0.08, breadth 0.16.

Habitat.—Central Pacific, Station 263, depth 2650 fathoms.

2. Coronidium diadema, n. sp. (Pl. 82, fig. 8).

Frontal ring kidney-shaped, one and a half times as broad as high, with a slight sagittal constriction. Sagittal ring ovate, smaller, about of the same size as the elliptical basal ring. Rods of all three rings cylindrical, bearing numerous short and stout curved spines, partly simple, partly branched. Four bunches of larger spines on the four corners of the basal ring, and one very large bunch on the apical pole. Basal gate elliptical, one and a half times as broad as long.

Dimensions.—Height of the frontal ring 0.13, breadth 0.18.

Habitat.—Indian Ocean (Madagascar), Rabbe, surface.

3. Coronidium cervicorne, n. sp. (Pl. 82, fig. 1).

Frontal ring kidney-shaped, twice as broad as high, one and a half times as broad as the elliptical basal ring, both with a slight sagittal constriction. Sagittal ring ovate. All three rings (in the figure seen from the apical pole) with cylindrical rods, armed with numerous stout spines, branched like a deer's antler. Basal gate rather oblong, twice as broad as long.

Dimensions.—Height of the frontal ring 0.08, breadth 0.16.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

4. Coronidium acacia, n. sp. (Pl. 82, fig. 2).

Frontal ring and sagittal ring nearly circular, of equal size, truncated at the base. Basal ring circular, somewhat smaller. All three rings with prominent edges, bearing bunches of short and straight pointed spines, like those of an Acacia. Basal gate circular.

Dimensions.—Height of the frontal ring 0.12, breadth 0.14.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.

Genus 417. Acanthodesmia,^[36] J. Müller, 1856, Monatsber. d. k. preuss.

Definition.—Coronida with five large, partly latticed gates (four lateral and one basal). Skeleton composed of two incomplete, partly fenestrated meridional rings, and one complete basal ring.

The genus Acanthodesmia, the oldest known form of all Coronida, differs from the preceding Coronidium, its ancestral form, in the development of irregular loose lattice-work along the rings, and therefore bears to it the same relation that Zygostephanium does to Zygostephanus. The first species described by Johannes Müller, Acanthodesmia vinculata ("with five large gates between the bars of the shell") remains the true type of this genus; the second species described by him (Acanthodesmia dumetum) belongs to the Plectanida (Polyplecta).

1. Acanthodesmia vinculata, J. Müller.

Acanthodesmia vinculata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 30, Taf. i. figs. 4-6 (non 7).

Lithocircus vinculatus, J. Müller, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 484.

Frontal ring violin-shaped, one and a half times as broad as high, with a sagittal constriction. Sagittal ring ovate, smaller. The four gates between the two rings are partly fenestrated by a few thin threads, irregularly branched and connecting the two rings. A few short thorns are scattered here and there. Basal gate elliptical.

Dimensions.—Height of the frontal ring 0.12, breadth 0.18.

Habitat.—Mediterranean (Nice), Atlantic (Canary Islands), surface.

2. Acanthodesmia ceratospyris, n. sp.

Frontal ring violin-shaped, one and a half times as broad as high, with a deep sagittal constriction. Sagittal ring semicircular, half as high as the frontal ring. The four gates between the two rings are partly fenestrated by anastomosing branches of the numerous, irregularly branched spines, which cover all three rings. Basal gate nearly circular, smaller than the sagittal ring.

Dimensions.—Height of the frontal ring 0.08, breadth 0.12.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

3. Acanthodesmia corona, n. sp. (Pl. 93, fig. 5).

Frontal ring kidney-shaped, nearly twice as broad as high, with a flat sagittal constriction. Sagittal ring semicircular. The four gates between the two rings are partly fenestrated by an arachnoidal network, composed of thin, irregularly branched threads, arising from the rings. The edges of all three rings are armed with irregular thorns. Basal gate circular, larger than the sagittal ring.

Dimensions.—Height of the frontal ring 0.08, breadth 0.14.

Habitat.—Indian Ocean (Madagascar), Rabbe, surface.

4. Acanthodesmia mülleri, n. sp.

Frontal ring kidney-shaped with a deep sagittal constriction. Sagittal ring ovate. The four gates between the two rings irregularly fenestrated, with a few large polygonal meshes. Edges of the rings with a few scattered thorns. Basal gate violin-shaped.

Dimensions.—Height of the frontal ring 0.1, breadth 0.16.

Habitat.—Tropical Atlantic, Station 347, surface.

Subfamily 3. Eucoronida, Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with six large gates (four lateral and two basal gates). Skeleton composed of three rings perpendicular to one another, two of which are complete (the vertical sagittal, and the horizontal basal ring); the third is incomplete (the vertical frontal ring).

Genus 418. Eucoronis,^[37] Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with six large simple gates (four lateral and two basal). Skeleton composed of two complete rings (the sagittal and basal) and one incomplete (frontal) ring. Basal ring without typical feet.

The genus Eucoronis and the following two nearly allied genera (Plectocoronis and Podocoronis) compose together the important subfamily Eucoronida. In this typical main group of Coronida the shell is constantly composed of three rings and six gates. The vertical sagittal ring and the horizontal basal ring are complete (as in the Semantida); the vertical frontal ring is incomplete. Between these three rings remain six large open gates, the four upper (or lateral) are always much larger than the four lower (or basal gates). Eucoronis may be derived from Semantis by development of the frontal ring.

Subgenus 1. Acrocoronis, Haeckel, 1881, Prodromus, p. 445.

Definition.—Rings smooth or rough, armed with numerous short spines or thorns.

1. Eucoronis perspicillum, n. sp. (Pl. 82, fig. 6).

Frontal ring elliptical, twice as broad as high, with a slight constriction at the apical pole, armed with three pairs of short conical spines, one apical pair (near the constriction) and two lateral pairs (one upper and one lower pair). Sagittal ring of the same height, half the breadth and double the thickness, also armed with three pairs of spines (one basal, one dorsal, and one ventral pair).

Dimensions.—Height of the frontal ring 0.11, breadth 0.22.

Habitat.—Central Pacific, Stations 265 to 268, depth 2700 to 2900 fathoms.

2. Eucoronis lævigata, n. sp.

Frontal ring elliptical, smooth, one and a half times as broad as high, without sagittal constriction, with horizontal basal gates. Sagittal ring of the same height and thickness, also elliptical and smooth. No spines on either of the smooth rings.

Dimensions.—Height of the frontal ring 0.1, breadth 0.15.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

3. Eucoronis nephrospyris, n. sp. (Pl. 82, fig. 5).

Frontal ring kidney-shaped, in the upper half convex, in the lower concave, with a sagittal constriction (often much deeper than in the specimen figured). Sagittal ring ovate, about two-thirds as high as the frontal ring. Rods of both rings without edges, cylindrical, armed with numerous short conical thorns.

Dimensions.—Height of the frontal ring 0.1 to 0.12, breadth 0.15 to 0.18.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, many Stations, surface and at various depths.

4. Eucoronis angulata, n. sp. (Pl. 82, fig. 3).

Frontal ring violin-shaped, twice as broad as high, on the upper and the lower margin concave, with a deep sagittal constriction. Sagittal ring pentagonal, with straight horizontal basal rod, two-thirds as high as the frontal ring. Rods of both rings with sharp prominent edges, bearing numerous short pyramidal spines.

Dimensions.—Height of the frontal ring 0.09, breadth 0.17.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

Subgenus 2. Lithocoronis, Haeckel, 1881, Prodromus, p. 445.

Definition.—Rings armed with numerous large, branched or arborescent spines.

5. Eucoronis cervicornis, n. sp.

Frontal ring kidney-shaped, in the upper half convex, in the lower concave, with sagittal constriction. Sagittal ring ovate, two-thirds as high as the frontal ring. Both rings armed with numerous stout spines, irregularly branched like a deer's antler. (Very similar to Coronidium cervicorne, Pl. 82, fig. 1, which I formerly confounded with it, but differing in the complete sagittal ring, which in the latter form is incomplete and has lost its basal part.)

Dimensions.—Height of the frontal ring 0.12, breadth 0.2.

Habitat.—Central Pacific, Station 264, surface.

6. Eucoronis arborescens, n. sp.

Frontal ring kidney-shaped, with a deep sagittal constriction in the concave basal part. Sagittal ring ovate, half as high as the frontal ring. Both rings armed with numerous thin, richly branched and arborescent spines (branches much thinner and more numerous than in the preceding and following species).

Dimensions.—Height of the frontal ring 0.15, breadth 0.25.

Habitat.—Equatorial Atlantic, Station 247, surface.

7. Eucoronis challengeri, n. sp. (Pl. 82, fig. 4).

Lithocoronis challengeri, Haeckel, 1881, Prodromus, p. 445.

Frontal ring violin-shaped, one and a half times as broad as high, with a strong sagittal constriction. Sagittal ring nearly circular, two-thirds as high as the frontal ring. Both rings armed with numerous irregularly branched spines. (The specimen figured, with red central capsule and numerous xanthellæ, was observed living by me at the Canary Islands.)

Dimensions.—Height of the frontal ring 0.1 to 0.12, breadth 0.14 to 0.17.

Habitat.—Cosmopolitan; Atlantic, Indian, Pacific, surface and at various depths.

Genus 419. Plectocoronis,^[38] Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with six large, partly latticed gates (four lateral and two basal). Skeleton composed of two complete rings (the sagittal and basal) and one incomplete (frontal) ring. Basal ring without developed typical feet.

The genus Plectocoronis differs from the preceding Eucoronis, its ancestral form, in the development of loose irregular lattice-work along the two meridional rings, and therefore bears to it the same relation that Acanthodesmia does to Coronidium. If the lattice-work become more complete and close the gates, these Coronida pass over directly into Spyroidea (Zygospyrida).

1. Plectocoronis anacantha, n. sp.

Basal ring and frontal ring elliptical, without sagittal constriction. Sagittal ring ovate. The frontal and sagittal rings are bordered on both edges with an incomplete series of small irregular pores. All three rings smooth, without spines.

Dimensions.—Height of the frontal ring 0.1, breadth 0.16.

Habitat.—Central Pacific, Station 274, depth 2750 fathoms.

2. Plectocoronis triacantha, n. sp.

Basal ring and frontal ring nearly circular, without sagittal constriction. Sagittal ring elliptical, prolonged at the apex into an apical horn from which two branched lateral bows descend and unite with the uppermost parts of the frontal ring. Four other small bows descend from the lowermost parts of the latter and unite with the basal ring. From the lateral corners of the basal ring descend two short vertical feet. (May be regarded as derived from Podocoronis toxarium, Pl. 83, Fig. 7, by development of the bows connecting the rings.)

Dimensions.—Height of the frontal ring 0.11, breadth 0.13.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

3. Plectocoronis pentacantha, n. sp. (Pl. 93, fig. 6).

Basal ring and frontal ring kidney-shaped, with deep sagittal constriction. Sagittal ring ovate, prolonged at the apex into an oblique horn. From the edges of the angular rings delicate threads arise, which anastomose and form irregular arachnoidal meshes, partly closing the four open lateral gates. Two basal gates simple. From the four nodal points of the basal ring there arise four, short diverging feet, comparable to rudimentary cortinar feet (two lateral from the frontal ring and two sagittal from the primary ring, as basal prolongations).

Dimensions.—Height of the frontal ring 0.12, breadth 0.18.

Habitat.—Central Pacific, Station 271, surface.

Genus 420. Podocoronis,^[39] Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with six large gates (four lateral and two basal). Skeleton composed of two complete rings (the sagittal and basal) and one incomplete (frontal) ring. Basal ring provided with typical, regularly disposed, descending feet (cortinar feet).

The genus Podocoronis differs from the two preceding nearly allied genera in the development of typical radial feet on the basal ring, which by their regular disposition and their general appearance among the Spyroidea and Cyrtoidea obtain great morphological importance. According to the different number and disposition of these basal feet (or "cortinar feet"), the following subgenera may be distinguished (regarded in my Prodromus, 1881, p. 445, as separate genera):—Dipocoronis with two lateral feet, Tripocoronis with three cortinar feet (most important!), Tetracoronis with four crossed feet, Hexacoronis with six radial feet, Stylocoronis with numerous (8 or more feet). These subgenera have important relations to the corresponding genera of Zygospyrida.

Subgenus 1. Dipocoronis, Haeckel, 1881, Prodromus, p. 445.

Definition.—Basal ring with two descending lateral feet (right and left) as prolongations of the frontal ring.

1. Podocoronis dipodiscus, n. sp.

Basal ring nearly circular, with two conical, straight, parallel descending feet, which are direct lateral prolongations of the subcircular frontal ring, and half as long as it. The ovate sagittal ring bears at the apex a short conical vertical horn. All rings nearly smooth.

Dimensions.—Height of the frontal ring 0.12, breadth 0.14.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

2. Podocoronis toxarium, n. sp. (Pl. 83, fig. 7).

Basal ring elliptical, with two descending, slightly curved conical feet, lateral prolongations of the subcircular frontal ring. The ovate sagittal ring bears at the apex a cylindrical vertical horn, which is connected by two descending lateral arches (or galear arches) with the uppermost part of the frontal ring.

Dimensions.—Height of the frontal ring 0.1, breadth 0.13.

Habitat.—Central Pacific, Stations 265 to 268, depth 2900 fathoms.

Subgenus 2. Tripocoronis, Haeckel, 1881, Prodromus, p. 445.

Definition.—Basal ring with three descending feet (one caudal and two pectoral).

3. Podocoronis cortiniscus, n. sp. (Pl. 97, fig. 2).

Basal ring violin-shaped, with three straight divergent thorny feet, about as long as the ovate sagittal ring. The dorsal part of the latter is straight, vertical, and prolonged downwards into the caudal foot, upwards into a stout, thorny, vertical apical horn. The ventral part is semicircular and gives off the lateral branches, forming the kidney-shaped sagittal ring. All the rings and their apophyses are armed with stout thorns. This and the following tripodal species may be directly derived from Cortina.

Dimensions.—Height of the frontal ring 0.1, breadth 0.15.

Habitat.—Central Pacific, Station 274, depth 2750 fathoms.

4. Podocoronis tripodiscus, n. sp.

Basal ring kidney-shaped, with three large divergent curved feet, nearly twice as long as the semicircular sagittal ring. The straight dorsal part of the latter is prolonged downwards into the caudal foot, upwards into a large branched apical horn, curved backwards. Differs from the preceding species mainly in the longer curved apophyses and in the larger violin-shaped frontal ring.

Dimensions.—Height of the frontal ring 0.12, breadth 0.2.

Habitat.—North Pacific, Station 238, surface. Fossil in Barbados.

Subgenus 3. Tetracoronis, Haeckel, 1881, Prodromus, p. 445.

Definition.—Basal ring with four descending feet (two sagittal and two lateral).

5. Podocoronis tetrapodiscus, n. sp.

Basal ring kidney-shaped, with four stout and straight divergent feet, about as long as the sagittal ring; two of them are lateral and arise from the basal corners of the violin-shaped frontal ring (at its junction with the basal ring); two are sagittal, and arise from the basal corners of the semicircular sagittal ring (one posterior caudal and one anterior sternal). The straight dorsal part of the sagittal ring is prolonged upwards into an apical horn. All the rings are thorny.

Dimensions.—Height of the frontal ring 0.15, breadth 0.25.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

Subgenus 4. Hexacoronis, Haeckel

Definition.—Basal ring with six radial descending feet (two sagittal, two pectoral, and two tergal feet).

6. Podocoronis hexapodiscus, n. sp.

Basal ring violin-shaped, with six conical, vertically descending feet, half as long as the sagittal ring; two of them are sagittal (arising from the two basal corners of the sagittal ring, caudal and sternal feet); the other four are lateral, and prolongations of the forked basal parts of the frontal ring, which is inserted on the basal ring with two forked branches; the anterior correspond to the pectoral, the posterior to the tergal feet of Hexaspyris. All the rings are thorny.

Dimensions.—Height of the frontal ring 0.11, breadth 0.17.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

Subgenus 5. Stylocoronis, Haeckel.

Definition.—Basal ring with numerous (eight to twelve or more) descending feet.

7. Podocoronis petalospyris, n. sp.

Basal ring violin-shaped, with ten to twelve flat lamellar, vertically descending feet, about as long as the ovate sagittal ring. Frontal ring twice as broad as long, elliptical. All rings nearly smooth. Similar to a Petalospyris without lattice-work.

Dimensions.—Height of the frontal ring 0.1, breadth 0.2.

Habitat.—Fossil in Barbados.

8. Podocoronis polypodiscus, n. sp.

Basal ring elliptical, with fifteen to eighteen conical, curved, descending feet, half as long as the ovate sagittal ring. Frontal ring kidney-shaped, one and a half times as broad as long. All the rings armed with short conical spines.

Dimensions.—Height of the frontal ring 0.12, breadth 0.18.

Habitat.—Central Pacific, Station 273, depth 2350 fathoms.

Subfamily 4. Trissocyclida, Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with eight large gates (four superior lateral and four inferior basal). Skeleton composed of three complete rings, perpendicular to one another; two of which are vertical (the primary or sagittal and the secondary or frontal ring), the third is horizontal (the tertiary or basal ring).

Genus 421. Tristephanium,^[40] Haeckel, 1881, Prodromus, p. 445.

Definition.—Coronida with eight large, simple gates of different sizes; the four upper or lateral gates larger than the four lower or basal gates. Skeleton composed of three simple complete rings, perpendicular to one another.

The genus Tristephanium, and the three following genera derived from it, represent together the interesting subfamily of Trissocyclida (Prodromus, 1881, p. 446). These differ from all other Coronida in the possession of three complete rings, perpendicular to one another. The first of these is the vertical sagittal ring, the second the vertical frontal ring, and the third the horizontal basal ring. Since these three rings lie in the three dimensive planes, they are perpendicular to one another; and between them remain eight large open gates. Originally the four upper or lateral gates (corresponding to those of Zygostephanus) are much larger, the four lower or basal gates (corresponding to those of Semantrum) much smaller; but afterwards the latter may reach the size of the former, so that the basal ring becomes equatorial (in Trissocircus and Trissocyclus). The common ancestral form of the Trissocyclida (Tristephanium) may be derived directly either from Semantrum (by complete development of the frontal ring) or from Eucoronis (by complete development of four basal gates).

Subgenus 1. Triostephus, Haeckel, 1881, Prodromus, p. 445.

Definition.—Sagittal and frontal ring of different size and form.

1. Tristephanium dimensivum, n. sp. (Pl. 93, fig. 9).

Sagittal ring ovate, with a large thorny apical horn, smaller than the two other rings. Frontal ring violin-shaped, with a deep sagittal constriction. Basal ring also violin-shaped, in the sagittal axis constricted. Its four gates (two jugular and two cardinal) of nearly equal size. All three rings angular, armed with scattered, stout, thorny spines, which are larger in the basal half.

Dimensions.—Height of the frontal ring 0.08, breadth 0.12.

Habitat.—North Pacific, Station 241, depth 2300 fathoms.

2. Tristephanium octopyle, n. sp. (Pl. 93, fig. 8).

Sagittal ring ovate, nearly smooth, smaller than the two other rings. Frontal ring kidney-shaped, with a deep basal constriction. Basal ring violin-shaped. The jugular gates about half as large as the cardinal gates. Rods of the rings cylindrical, with few scattered thorns.

Dimensions.—Height of the frontal ring 0.09, breadth 0.14.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

3. Tristephanium hertwigii, Haeckel.

Acanthodesmia hertwigii, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. pp. 499, 539, Taf. xxxii. figs. 9a-9c.

Sagittal ring ovate or nearly semicircular; its dorsal rod straight, smooth (fig. 9c, a), its ventral rod (b) curved, thorny. Frontal ring much larger, thorny, violin-shaped, with a slight sagittal constriction. Basal ring smaller than the sagittal ring, thorny, kidney-shaped, with four different gates; the two cardinal pores much larger than the two jugular pores. (The four basal pores are often much larger than in the specimen figured by Bütschli. Also the number, form, and size of the spines is very variable.)

Dimensions.—Height of the frontal ring 0.07 to 0.09, breadth 0.17 to 0.2.

Habitat.—Fossil in Barbados.

Subgenus 2. Tristephaniscus, Haeckel, 1881, Prodromus, p. 445.

Definition.—Sagittal and frontal ring of equal size and form.

4. Tristephanium quadricorne, n. sp. (Pl. 93, fig. 7).

Sagittal and frontal ring of equal size and form, larger than the circular basal ring. From the four corners, in which the latter crosses the two former, arise four strong, divergent spines, branched like a deer's antler. Some smaller spines are scattered on the rings, and a bunch of four spines arises on the apical pole. The four upper gates are triangular, the four lower nearly semicircular, the latter of equal size, half as large as the former.

Dimensions.—Height of the frontal ring 0.13, breadth 0.14.

Habitat.—South Atlantic, Station 342, depth 1445 fathoms.

Genus 422. Tricyclidium,^[41] Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with eight large, partly fenestrated gates; the four upper or lateral gates larger than the four lower or basal gates. Skeleton composed of three latticed complete rings, perpendicular to one another.

The genus Tricyclidium differs from the preceding Tristephanium, its ancestral form, in the development of loose rudimentary lattice-work along the rings, and therefore bears to it the same relation that Plectocoronis does to Eucoronis. It may pass directly over into Dictyospyris.

1. Tricyclidium dictyospyris, n. sp. (Pl. 93, fig. 13).

Sagittal ring ovate, twice as thick as the two other larger rings, which become very thin, thread-like at the lateral junction, and are both slightly violin-shaped, in the middle sagittal plane constricted; the frontal ring larger than the basal. All three rings bear small scattered spines, which are irregularly branched, and by anastomoses of the thread-like branches form small irregular meshes along the rings. The four basal gates are of equal size.

Dimensions.—Height of the frontal ring 0.11, breadth 0.15.

Habitat.—Equatorial Atlantic, Station 347, depth 2250 fathoms.

2. Tricyclidium semantrum, n. sp.

Sagittal ring ovate, smaller than the violin-shaped frontal ring and larger than the elliptical basal ring. All three rings of nearly equal thickness, armed with short irregular branches, which are partly connected, and forming small irregular meshes along the rings. The four basal gates are of different sizes; the two anterior (jugular) gates only half as large as the two posterior (cardinal) gates.

Dimensions.—Height of the frontal ring 0.12, breadth 0.18.

Habitat.—South Atlantic, Station 348, depth 2450 fathoms.

Genus 423. Trissocircus,^[42] Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with eight large simple gates of equal size. Skeleton composed of three simple complete rings, perpendicular to one another.

The genus Trissocircus, and the following nearly allied Trissocyclus, differ from the two preceding ancestral genera in the remarkable growth of the four basal gates, which reach the size of the lateral gates. Therefore both hemispheres of the shell (the upper or apical and the lower or basal) here become equal and the basal ring becomes equatorial. Sometimes even all three rings attain the same size, so that it is difficult or impossible to distinguish them. In this curious case the Coronida exhibit a striking resemblance to some Sphæroidea.

Subgenus 1. Tricircarium, Haeckel.

Definition.—Sagittal ring smaller than the two other rings, which are both elliptical.

1. Trissocircus lentellipsis, n. sp. (Pl. 93, fig. 10).

All three rings elliptical, of different sizes, smooth, without spines. The sagittal ring is the smallest, but two to three times as thick as the other two rings, which have the larger (transverse) axis common. The smaller (sagittal) axis of the sagittal ring is also the smaller axis of the equatorial ring, whilst the larger (principal) axis of the former is the smaller axis of the frontal ring.

Dimensions.—Height of the frontal ring 0.07, breadth 0.1.

Habitat.—Western Tropical Pacific, Station 224, depth 1850 fathoms.

2. Trissocircus binellipsis, n. sp. (Pl. 83, fig. 6).

Sagittal ring circular, smaller than the other two rings, which are both equal, elliptical, slightly constricted on the poles of the principal and transverse axes. The axis of the circular sagittal ring is the shorter axis of the frontal and equatorial ring, and about half as long as their longer axis. All three rings smooth, without spines.

Dimensions.—Height of the frontal ring 0.08, breadth 0.12.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

3. Trissocircus octostoma (Pl. 93, fig. 11).

Sagittal ring circular, smaller than the other two rings, which are both equal, elliptical, distinctly constricted at the poles of the principal and transverse axes. The axis of the circular sagittal ring is the shorter axis of the frontal and equatorial ring, about one-third shorter than their longer axis. All three rings armed with short, irregularly branched spines.

Dimensions.—Height of the frontal ring 0.1, breadth 0.12.

Habitat.—Indian Ocean, Ceylon (Belligemma), Haeckel, surface.

Subgenus 2. Tricirconium, Haeckel.

Definition.—All three rings equal, circular.

4. Trissocircus octahedrus, n. sp.

All three rings equal, circular, smooth, their rods cylindrical (in the transverse section circular). From each pole of the three equal axes arises a short conical spine; these six spines correspond to the six corners of a regular octahedron.

Dimensions.—Diameter of all three rings 0.08, thickness 0.006.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

5. Trissocircus globus, n. sp. (Pl. 82, fig. 13).

All three rings equal, circular, thorny; their rods prismatic (in the transverse section triangular), with three sharp dentated edges and scattered branched thorns. From each pole of the three equal axes (which correspond to the three axes of a regular octahedron) arises a bunch of larger spines.

Dimensions.—Diameter of all three rings 0.12, thickness 0.01.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

Genus 424. Trissocyclus,^[43] Haeckel, 1881, Prodromus, p. 446.

Definition.—Coronida with eight large, partly fenestrated gates of equal size. Skeleton composed of three complete latticed rings, perpendicular to one another.

The genus Trissocyclus differs from its nearly allied ancestral form Trissocircus only in the development of small anastomosing branches along the edges of the rings. The incomplete lattice-work, produced by these anastomoses, partly protects the eight large gates. The three rings are either of equal or of different sizes.

Subgenus 1. Tricyclarium, Haeckel.

Definition.—Sagittal ring circular, smaller than the other two rings, which are both elliptical.

1. Trissocyclus stauroporus, n. sp. (Pl. 83, fig. 5).

Sagittal ring circular, smaller than the other two equal elliptical rings. On each of the six corners (or crossing points of every two rings) are developed four small pores, forming a cross around the poles of the three axes. All three rings smooth, without spines.

Dimensions.—Height of the frontal ring 0.09, breadth 0.13.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

2. Trissocyclus triaxonius, n. sp.

Sagittal ring circular, smaller than the two other equal elliptical rings. From the edges of all three rings are developed small branches, which by irregular ramification and anastomoses form small irregular meshes along the rings. Similar to Trissocircus octostoma, but with thicker rings; it may be developed from the latter species by connection of the branches which border the rings.

Dimensions.—Height of the frontal ring 0.12, breadth 0.15.

Habitat.—South Pacific, Station 298, depth 2225 fathoms.

Subgenus 2. Tricyclonium, Haeckel.

Definition.—All three rings equal, circular.

3. Trissocyclus sphæridium, n. sp. (Pl. 93, fig. 12).

All three rings equal, circular, thorny; their rods prismatic, three-sided, with three denticulate edges; the teeth of the lateral edges become branched, and form by anastomoses of the branches small irregular meshes, which partly protect the eight large open gates.

Dimensions.—Diameter of the three rings 0.16, thickness 0.012.

Habitat.—Indian Ocean, Belligemma, Ceylon (Haeckel), surface

Family LI. Tympanida, Haeckel.

Definition.—Stephoidea with two parallel horizontal rings, an upper mitral and a lower basal ring; both connected by complete or incomplete vertical rings, or by parallel vertical columellæ.

The family Tympanida (or Parastephida) differs from the other Stephoidea in the development of two horizontal rings, which lie in horizontal planes and arise from the upper and the lower poles of the primary sagittal ring. Therefore the same formation, which we found in the Semantida on the basal pole only of the main axis, here takes place also on its apical pole. On both poles arise at each side from the sagittal ring two corresponding pairs of curved branches: the lateral ends of the opposite branches (dorsal and ventral branch) become united in the frontal plane and so form two complete horizontal rings. The upper ring, composed of the superior or mitral branches, may be called the mitral ring, the lower ring, formed by the inferior or basal branches, the basal ring. Both rings are commonly of nearly equal size, more rarely of different sizes. Their connection is effected either by the primary (sagittal) ring only, or also by secondary vertical rings, a frontal ring in the lateral plane, or some diagonal meridian rings between the latter and the former. These vertical rings, which connect both horizontal rings in the form of "columellæ," may be either complete or incomplete; in the latter case their apical and basal parts are lost, the dorsal and ventral parts only being preserved.

The Tympanida develop a great variety of different forms, greater than in the three other families of Stephoidea, so that we may distinguish here not less than sixteen genera and seventy-two species. Hitherto only three species were known: Prismatium tripleurum, figured in 1862 in my Monograph, Tympanidium barbadense, figured by Bury in the "fossil Polycystins of Barbados," and Tympaniscus fibula, described in 1875 by Ehrenberg as a Ceratospyris fibula. The number of species in this large and richly developed group will be considerably augmented by further researches. A great many of them exhibit remarkable relations to different Nassellaria. For better survey of the whole family we distinguish here four subfamilies, the first of which (Protympanida) is probably the common ancestral group of the other three. They may have been derived originally either from the Semantida or directly from the Stephanida.

The first subfamily, Protympanida, exhibits a complete primary or vertical sagittal ring, bearing on the upper part a horizontal mitral ring, on the lower part a horizontal basal ring. Therefore the gates of these two parallel rings become bisected by the sagittal ring, each divided into a right and a left half. The sagittal ring itself becomes divided by the two horizontal rings into four parts or rods; two opposite of these are more or less vertical; the dorsal (posterior) and the ventral (anterior) rod; the two other rods are more or less horizontal; the mitral (upper) and the basal (lower) rod.

In Protympanium (Pl. 93, fig. 14), the simplest and most primitive form of Tympanida, the connection of the two horizontal rings is effected only by the dorsal and ventral rods of the sagittal ring forming two parallel more or less vertical "columellæ." In all other Protympanida accessory columellæ are developed between the latter. In the greater number we find two secondary columellæ in the lateral plane, being the lateral segments of an incomplete frontal ring (Acrocubus, Pl. 93, figs. 15-17). Between the latter and the former there are sometimes developed four tertiary columellæ, as segments of two crossed incomplete diagonal rings (Tympanidium, Pl. 94, figs. 1, 18). At other times we find six columellæ; here probably the frontal ring is cleft into halves on each side (Tympaniscus, Pl. 94, figs. 4-7). Some genera are distinguished by the development of an equatorial ring, or a third horizontal ring (between the upper mitral and the lower basal ring); this equatorial ring is either complete (Microcubus Pl. 94, figs. 8-10) or incomplete, developed only laterally (Octotympanum, Pl. 94, figs. 2, 3). The genus Toxarium (Pl. 93, figs. 18-20) is distinguished by the development of accessory pairs of bows in the frontal plane, upper or galear bows and lower or thoracal bows, remarkable as beginnings of the accessory joints, which we distinguish in many Spyroidea and Cyrtoidea as "galea and thorax."

The second subfamily of Tympanida are the Paratympanida, in which the two horizontal rings become closed by lattice-work. The numerous columellæ connecting the two rings are here either divergent (Paratympanum, with two unequal rings, Pl. 94, fig. 14) or parallel and vertical (Lithotympanum, with two equal rings, Pl. 83, fig. 1). The shell of the latter assumes the form of a drum.

A third small subfamily, Dystympanida, is represented by a single genus only, Dystympanium (Pl. 94, figs. 15, 16). Here only the upper or mitral ring is closed by lattice-work, whilst the lower or basal ring exhibits quite a simple opening, a large "basal gate" which has probably arisen by loss of the basilar rod of the sagittal ring. These curious forms exhibit a remarkable resemblance to some Monocyrtida, and also to the Dictyocha (Phæodaria).

The fourth subfamily, the Eutympanida, are distinguished by the simple wide aperture of the two horizontal rings; the upper enclosing a simple "mitral gate," the lower a simple "basal gate." Here probably the two horizontal parts of the sagittal ring (the upper mitral rod and the lower basilar rod) are lost by reduction; its two vertical parts (the dorsal and ventral rods) only remaining and forming the two parallel columellæ, which connect the two horizontal rings (Parastephanus, Pl. 93, fig. 21). In this group also secondary columellæ are commonly developed between the two rings, alternating with the two primary columellæ. Pseudocubus (Pl. 94, figs. 11, 12), resembling an obelisk, exhibits four divergent columellæ; the two sagittal of these are probably the vertical parts of the primary ring, whilst the two lateral are the halves of an incomplete frontal ring. In Lithocubus (Pl. 82, fig. 12) the four columellæ are parallel and vertical, the two rings being equal; the shell here assumes the form of a geometrical cube. Prismatium is distinguished by three parallel columellæ; two of these are probably parts of a frontal ring, whilst the third is the remains of a reduced sagittal ring. In Circotympanum (Pl. 94, fig. 17) and in Lithotympanum (Pl. 82, fig. 11) the number of the columellæ is augmented, there being six to eight or more; in the former they are divergent (the two rings being of different sizes), in the latter parallel (the two rings being equal); the fundamental form of the former is a truncated pyramid, of the latter a prism.

Comparing these differences between the four subfamilies of Tympanida, we may suppose that the common ancestral group are the Protympanida, derived from the Semantida by the formation of a mitral ring. If the two horizontal rings become closed by lattice-work, the Paratympanida arise. When the mitral ring only becomes latticed, the basal ring being simple, the Dystympanida originate. Finally, the fourth subfamily, the Eutympanida, may be derived from the Protympanida by the loss of the two horizontal parts of the sagittal ring.

The two horizontal rings (upper mitral and lower basal) and the two vertical rings (primary sagittal and secondary frontal), which thus compose the loose framework of the Tympanida, are rarely smooth, commonly armed with spines or branches, similar to those of the Coronida. The rods or bars are either roundish (with circular transverse section) or angular (commonly with triangular transverse section). The paired branches of the two vertical rings often preserve the characteristic arrangement inherited from the Semantida and Stephanida. The two horizontal rings sometimes exhibit typical apophyses, which recur in the Spyroidea and Cyrtoidea. The mitral ring may possess one odd apical horn and two paired frontal horns (Pl. 93, figs. 16, 17, 19, 23). The basal ring sometimes bears the three typical feet of Cortina (Pl. 93, figs. 16, 22), one odd caudal foot and two paired pectoral feet. Sometimes a fourth (sternal) foot is developed (Pl. 94, fig. 4), at other times only two lateral feet (Pl. 94, figs. 5, 6).

Synopsis of the Genera of Tympanida.

I. Subfamily Protympanida. Two horizontal rings (upper mitral ring and lower basal ring) bisected by the complete sagittal ring. Two horizontal rings connected by two columellæ. One complete sagittal ring (no frontal ring), 425. Protympanium.

Two horizontal rings connected by four columellæ (the halves of the sagittal and the frontal ring). No equatorial ring. No galear and thoracal bows, 426. Acrocubus.

Galear and thoracal bows, 427. Toxarium.

An equatorial ring. Equatorial ring complete, 428. Microcubus.

Equatorial ring incomplete, 429. Octotympanum.

Two horizontal rings connected by six or eight columellæ (three or four vertical rings). Six columellæ (three meridional rings), 430. Tympaniscus.

Eight columellæ (four meridional rings), 431. Tympanidium.

II. Subfamily Paratympanida. Two horizontal rings fenestrated. Two horizontal rings closed by a lattice-plate, connected by numerous columellæ. Two rings unequal (columellæ divergent), 432. Paratympanum.

Two rings equal (columellæ parallel), 433. Lithotympanum.

I. Subfamily Protympanida. Two horizontal rings (upper mitral ring and lower basal ring) bisected by the complete sagittal ring.

Two horizontal rings connected by two columellæ.

One complete sagittal ring (no frontal ring),

425. Protympanium.

Two horizontal rings connected by four columellæ (the halves of the sagittal and the frontal ring).

No equatorial ring.

No galear and thoracal bows,

426. Acrocubus.

Galear and thoracal bows,

427. Toxarium.

An equatorial ring.

Equatorial ring complete,

428. Microcubus.

Equatorial ring incomplete,

429. Octotympanum.

Two horizontal rings connected by six or eight columellæ (three or four vertical rings).

Six columellæ (three meridional rings),

430. Tympaniscus.

Eight columellæ (four meridional rings),

431. Tympanidium.

II. Subfamily Paratympanida. Two horizontal rings fenestrated.

Two horizontal rings closed by a lattice-plate, connected by numerous columellæ.

Two rings unequal (columellæ divergent),

432. Paratympanum.

Two rings equal (columellæ parallel),

433. Lithotympanum.

III. Subfamily Dystympanida. Mitral ring fenestrated, basal ring simple.

Two horizontal rings connected by numerous (six to eight or more columellæ).

Mitral ring closed by a lattice-plate, basal ring simple,

434. Dystympanium.

IV. Subfamily Eutympanida. Two horizontal rings (upper mitral ring and lower basal ring) simple. Apical and basal parts of the sagittal ring lost.

Two horizontal rings connected by two or three columellæ (four or five open gates).

Two columellæ (parts of the sagittal ring),

435. Parastephanus.

Three columellæ (parts of the half sagittal and the frontal ring),

436. Prismatium.

Two horizontal rings connected by four or more columellæ (six or eight or more open gates).

Four columellæ

Two rings unequal,

437. Pseudocubus.

Two rings equal,

438. Lithocubus.

Six to eight or more columellæ.

Two rings unequal,

439. Circotympanum.

Two rings equal,

440. Eutympanium.

III. Subfamily Dystympanida. Mitral ring fenestrated, basal ring simple. Two horizontal rings connected by numerous (six to eight or more columellæ). Mitral ring closed by a lattice-plate, basal ring simple, 434. Dystympanium.

IV. Subfamily Eutympanida. Two horizontal rings (upper mitral ring and lower basal ring) simple. Apical and basal parts of the sagittal ring lost. Two horizontal rings connected by two or three columellæ (four or five open gates). Two columellæ (parts of the sagittal ring), 435. Parastephanus.

Three columellæ (parts of the half sagittal and the frontal ring), 436. Prismatium.

Two horizontal rings connected by four or more columellæ (six or eight or more open gates). Four columellæ Two rings unequal, 437. Pseudocubus.

Two rings equal, 438. Lithocubus.

Six to eight or more columellæ. Two rings unequal, 439. Circotympanum.

Two rings equal, 440. Eutympanium.

Subfamily 1. Protympanida, Haeckel.

Definition.—Tympanida with two bisected horizontal rings, connected by the complete vertical sagittal ring. (The upper mitral ring and the lower basal ring become divided by the complete primary or sagittal ring into two horizontal symmetrical gates, two mitral gates on the apical and two basal gates on the basal pole.)

Genus 425. Protympanium,^[44] Haeckel, 1881, Prodromus, p. 447 (sensu emend.).

Definition.—Tympanida with two bisected horizontal rings, connected by two vertical columellæ.

The genus Protympanium, is the most simple form of all Tympanida, and probably the common ancestral form of this family. It arises from Lithocircus by the development of two horizontal rings, perpendicular to the primary sagittal ring. The upper or mitral ring arises by lateral union of two pairs of superior branches, the lower or basal ring by union of two pairs of basal branches of the primary vertical ring.

1. Protympanium primordiale, n. sp.

Mitral and apical ring of equal size, elliptical, smooth, somewhat smaller than the connecting thorny sagittal ring.

Dimensions.—Diameter of the two horizontal rings 0.12, of the sagittal ring 0.15.

Habitat.—Central Pacific, Stations 263 to 274, at various depths.

2. Protympanium amphipodium, n. sp. (Pl. 93, fig. 14).

Mitral and apical rings of equal size, thin, elliptical, smooth, larger than the broad connecting sagittal ring. The latter bears on the apical and on the basal pole two divergent straight spines (lying in the frontal plane), the two apical (or horns) somewhat smaller and not so spiny as the two basal spines (or feet). In the frontal plane there arise from the two horizontal rings on each side two small opposite spines (remnants or beginnings of the lateral frontal ring?).

Dimensions.—Diameter of the two horizontal rings 0.11, of the sagittal ring 0.07.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

3. Protympanium trissocircus, n. sp.

Mitral ring smaller than the basal ring; both rings circular, rough. Sagittal ring in size between the two former. All three rings covered with very small thorns.

Dimensions.—Diameter of the mitral ring 0.08, of the sagittal ring 0.1, of the basal ring 0.12.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

Genus 426. Acrocubus,^[45] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two bisected horizontal rings, connected by four vertical columellæ. No equatorial ring.

The genus Acrocubus is the most primitive of those remarkable Tympanida, the skeleton of which represents more or less exactly the form of a geometrical cube. A simple complete sagittal ring bears on the superior and on the inferior part two opposite pairs of lateral branches; by union of the convergent branches of each side there arise two horizontal parallel quadrangular rings, which are bisected by the sagittal ring. Therefore the superior ring encloses two triangular mitral gates, the inferior two triangular basal gates. The lateral corners of the two gates of each side are connected by a vertical rod or columella. These two parallel columellæ are the remaining middle parts of the secondary or frontal ring, which is incomplete on the superior and on the inferior face of the body. If the sagittal ring also become incomplete, by the loss of the superior and inferior part (the anterior and posterior only remaining), then Acrocubus is transformed into Lithocubus.

Subgenus 1. Apocubus, Haeckel.

Definition.—Basal ring without descending feet.

1. Acrocubus octopylus, n. sp. (Pl. 82, fig. 9).

Mitral ring somewhat smaller than the basal ring; both rings rhombic, with curved outlines. Sagittal ring elliptical, with six pairs of nodulate protuberances. Four columellæ curved. Nodal points without radial spines.

Dimensions.—Height of the frontal ring 0.12, breadth 0.18.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

2. Acrocubus tesseralis, n. sp.

Mitral ring of the same size as the basal ring; both rings square, smooth, with straight outlines. Sagittal ring also square, smooth. Four columellæ straight. Nodal points without radial spines. The shell has the form of a regular geometrical cube, the edges of which are represented by the rings.

Dimensions.—Height of the frontal ring 0.1, breadth 0.11.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.

Subgenus 2. Dipocubus, Haeckel.

Definition.—Basal ring with two descending feet.

3. Acrocubus brachiatus, n. sp.

Mitral ring smaller than the basal, both rings square, with thick straight rods. Sagittal ring tuberculate, square, equatorial part thinner. Four columellæ curved, the two lateral ones prolonged downwards into two vertical parallel straight feet of half their length.

Dimensions.—Diameter of the cube 0.12; length of the feet 0.06.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

4. Acrocubus amphistylus, n. sp.

Mitral and basal rings of nearly equal size, square, with thick curved rods. Sagittal ring elliptical, in the equatorial part thinner. Frontal ring tuberculate. Four columellæ curved, the two lateral ones prolonged downwards into two vertical, tuberculate feet of half their length.

Dimensions.—Diameter of the cube 0.13; length of the feet 0.07.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

5. Acrocubus arcuatus, n. sp. (Pl. 93, fig. 15).

Mitral and basal rings, as well as the sagittal ring, of the same form as in the preceding nearly allied species. The two lateral columellæ are prolonged not only downwards into two short vertical feet, but also upwards into two curved bows, which are united in a vertical ascending horn, arising from the apical pole of the sagittal ring.

Dimensions.—Diameter of the cube 0.14; total height 0.21.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

Subgenus 3. Tripocubus, Haeckel.

Definition.—Basal ring with three descending feet (one odd caudal and two paired lateral).

6. Acrocubus lasanum, n. sp.

Mitral ring smaller than the basal, both rings square, with curved rods. Sagittal ring ovate, prolonged upwards into an occipital simple horn, downwards into a caudal foot. Two lateral columellæ prolonged downwards into two pectoral feet. All three feet conical, about as long as the height of the cube.

Dimensions.—Diameter of the cube 0.08; length of the feet 0.07.

Habitat.—North Pacific, Station 241, depth 2300 fathoms.

7. Acrocubus cortina, n. sp. (Pl. 93, fig. 16).

Mitral ring smaller than the basal, both rings elliptical, with curved rods. Sagittal ring ovate, prolonged upwards into an occipital horn, downwards into a caudal foot, as in the preceding species. As in the latter, also, the two lateral columellæ are prolonged downwards into two pectoral feet, but also upwards into two convergent horns, which are united with the occipital horn (commencing the formation of a galea). Rings and feet somewhat thorny.

Dimensions.—Diameter of the cube 0.16; total height 0.2.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

Subgenus 4. Tetracubus, Haeckel.

Definition.—Basal ring with four descending feet (two sagittal and two lateral).

8. Acrocubus tetrapodius, n. sp.

Mitral and basal rings of the same size, square, with straight rods, sagittal ring also square. The four vertical columellæ are nearly parallel and straight, prolonged upwards into four short conical horns, downwards into four longer conical feet. (The shell has nearly the form of a geometrical cube, the eight corners of which are prolonged into eight vertical conical spines, four smaller ascending and four larger descending.)

Dimensions.—Diameter of the cube 0.09; length of the feet 0.06.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

9. Acrocubus amphithectus, n. sp. (Pl. 93, fig. 17).

Mitral ring smaller than the basal, both rings elliptical, with curved rods. Four columellæ thorny, also curved, divergent downwards, prolonged upwards into four thorny convergent horns, downwards into four larger branched divergent feet. The two sagittal horns and feet (anterior and posterior) are smaller than the two lateral (right and left); therefore the fundamental form of this species is distinctly amphithect (as in the Ctenophora).

Dimensions.—Breadth of the cube 0.12; total height 0.2.

Habitat.—South Pacific, Station 289, depth 2550 fathoms.

Genus 427. Toxarium,^[46] n. gen.

Definition.—Tympanida with two bisected horizontal rings, connected by four vertical columellæ. In the frontal plane two galear bows project upwards, and two thoracal bows downwards.

The genus Toxarium differs from its ancestral form Acrocubus in the development of two pairs of peculiar bows, placed in the lateral or frontal plane; the upper pair projects above the mitral gates, and may be called the "galear bows," the lower pair projects below the basal gates of the cubical shell, and may be called the "thoracal bows." Both pairs are produced originally by the development of two forked vertical spines, arising in the frontal plane on both poles of the principal axis from the sagittal ring (compare Protympanium amphipodium, Pl. 93, fig. 14). The apical fork-branches become connected with the lateral corners of the mitral gates, the basal branches with those of the basal gates. By development of lattice-work between the bows and the rings some Spyroidea (Amphispyris, &c.) may have arisen. The important genus Toxarium may be divided into three subgenera. In Toxellium all the bows are simple, in Toxonium, all are forked; in Toxidium, the galear bows are simple, the thoracal bows forked.

Subgenus 1. Toxellium, Haeckel.

Definition.—Galear and thoracal bows simple.

1. Toxarium circospyris, n. sp. (Pl. 88, fig. 1).

Galear and thoracal bows simple, of about the same size as the frontal bows between them; all bows armed with scattered simple conical spines. Sagittal constriction deep, half as long as the whole shell. Lateral outlines of the shell nearly parallel.

Dimensions.—Length of the shell 0.16, breadth 0.13.

Habitat.—Central Pacific, Stations 265 to 274, depth 2350 to 2925 fathoms.

2. Toxarium subcirculare, n. sp.

Galear and thoracal bows simple, armed with scattered simple spines of about equal size, smaller than the smooth frontal bows between them. Sagittal constriction very flat. Therefore the frontal perimeter of the shell is nearly circular.

Dimensions.—Length of the shell 0.15, breadth 0.14.

Habitat.—North Atlantic (Antilles), Weber, surface.

3. Toxarium thorax, n. sp. (Pl. 93, fig. 18).

Galear bows simple, smaller than the frontal bows, and these again smaller than the simple thoracal bows; therefore the shell increases in breadth towards the base, and resembles the skeleton of the thorax of one of the higher vertebrates (the bow-pairs corresponding to rib-pairs, the ventral part of the sagittal ring to the sternum, the dorsal part to the vertebral column). Sagittal constriction very deep. All bows are armed with scattered, irregularly branched spines.

Dimensions.—Length of the shell 0.17, breadth 0.2.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

4. Toxarium constrictum, n. sp.

Galear and thoracal bows simple, of nearly equal size, larger than the frontal bows between them. Therefore the shell is constricted in the equatorial plane. Sagittal constriction also deep. All bows armed with scattered, irregularly branched spines.

Dimensions.—Length of the shell 0.14, breadth 0.12.

Habitat.—North Pacific, Station 236, surface.

Subgenus 2. Toxidium, Haeckel.

Definition.—Galear bows simple, thoracal bows forked.

5. Toxarium cordatum, n. sp. (Pl. 93, fig. 19).

Galear bows simple, thoracal bows forked, both somewhat smaller than frontal bows; all bows armed with scattered simple conical spines, mostly developed at the thoracal bows. Both galear bows are united in a central vertical columella, which arises from the apex of the sagittal ring, and is prolonged into an apical horn. Therefore the sagittal constriction exists only in the basal half of the inversely cordate shell.

Dimensions.—Length of the shell 0.18, breadth 0.16.

Habitat.—South Atlantic, Station 348, depth 2450 fathoms.

6. Toxarium furcatum, n. sp.

Galear bows simple, thoracal bows forked, both somewhat broader than the frontal bows. Shell therefore slightly constricted in the equatorial plane. Sagittal constriction rather deep, equal in the apical and basal parts. All bows armed with scattered spines, which are partly simple, partly forked.

Dimensions.—Length of the shell 0.14, breadth 0.16.

Habitat.—Central Pacific, Station 270, depth 2925 fathoms.

7. Toxarium pedatum, n. sp.

Galear bows simple, smaller than the frontal bows, which are again smaller than the thoracal bows. Therefore the breadth of the shell increases towards the base. Sagittal constriction flat in the apical part, deep in the basal part. All bows armed with small irregularly scattered spines; at the base six larger divergent feet (two lateral, two anterior, and two posterior).

Dimensions.—Length of the shell 0.17, breadth 0.15.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

Subgenus 3. Toxonium, Haeckel.

Definition.—Galear and thoracal bows forked.

8. Toxarium costatum, n. sp.

Galear and thoracal bows forked, smaller than the frontal bows, all bows thorny, without larger spines. Sagittal constriction on both poles deep. Lateral outlines of the shell nearly parallel.

Dimensions.—Length of the shell 0.15, breadth 0.12.

Habitat.—Indian Ocean, Socotra (Haeckel), surface.

9. Toxarium bifurcum, n. sp. (Pl. 93, fig. 20).

Galear and thoracal bows forked, the former smaller than the frontal bows, the latter larger. Sagittal constriction rather flat on the apical pole, which bears a vertical forked horn, very deep on the basal pole of the primary ring. All bows armed with numerous spines, which are partly simple, partly forked, and mainly developed at the basal part of the thoracal bows.

Dimensions.—Length of the shell 0.2, breadth 0.2.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Genus 428. Microcubus,^[47] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two bisected horizontal rings, connected by four vertical columellæ, which are bisected again by an equatorial ring.

The genus Microcubus is derived from its ancestral form Acrocubus by development of a third horizontal ring, which lies in the equatorial plane, parallel to the upper mitral and the lower basal ring. Whilst these latter are both bisected by the complete vertical sagittal ring, the equatorial ring is complete, and connected at the poles of the sagittal axis with the principal ring, and at the poles of the transverse axis with the frontal ring. Therefore the shell exhibits not eight large gates as in Acrocubus, but twelve, viz., four horizontal gates (two superior mitral and two inferior basal), four upper vertical gates (between the mitral and the equatorial ring), and four lower vertical gates (between the basal and the equatorial ring).

1. Microcubus dodecastoma, n. sp. (Pl. 94, fig. 9).

All twelve gates simple, irregularly ovate or pentagonal. Frontal ring on the sides concave, constricted by the equatorial ring. All rings curved, armed with short irregular thorns. No larger basal spines.

Dimensions.—Length of the shell 0.13, breadth 0.15.

Habitat.—Central Pacific, Stations 271 to 274, depth 2350 to 2750 fathoms.

2. Microcubus pentacircus, n. sp.

All twelve gates simple. Frontal ring on the sides convex, not constricted by the equatorial ring. All rings tuberculate, with irregular roundish knots. No larger basal spines. Similar to the preceding species; but the five rings are much thicker and tuberculate (not thorny); the twelve gates are therefore relatively smaller.

Dimensions.—Length of the shell 0.1, breadth 0.12.

Habitat.—Fossil in Barbados.

3. Microcubus zonarius, n. sp. (Pl. 94, fig. 8).

All twelve gates simple, ovate. Frontal ring on the sides convex, not constricted by the equatorial ring, nearly twice as broad as long. All rings thorny, very thin, except only the broad angular sagittal ring. No larger basal spines.

Dimensions.—Length of the shell 0.08, breadth 0.15.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

4. Microcubus quadrupes, n. sp.

All twelve gates simple, square. Frontal ring square, not constricted by the equatorial ring. All rings smooth, quadrangular. Basal ring with four short vertical conical feet, two of which (right and left) are inferior prolongations of the frontal ring, and arise from the lateral corners of the basal gates; two others are prolongations of the sagittal ring (sternal and caudal), and arise from the medial corners of the basal gates. (The shell is like a small cube with four feet.)

Dimensions.—Length of the shell 0.13, breadth 0.11.

Habitat.—North Pacific, Station 253, depth 3125 fathoms.

5. Microcubus cornutus, n. sp.

Eight gates (two mitral, two basal, and four superior) simple; four inferior gates fenestrated by arachnoidal irregular threads. Frontal ring square, constricted on the sides by the equatorial ring. Basal ring with four short conical vertical feet, as in the preceding species. Sagittal ring with a vertical horn on the apex. All rings with small scattered thorns.

Dimensions.—Length of the shell 0.11, breadth 0.13.

Habitat.—North Pacific, Station 235, surface.

6. Microcubus amphispyris, n. sp. (Pl. 94, fig. 10).

Four gates (two mitral and two basal) simple; eight lateral gates (four superior and four inferior) fenestrated by arachnoidal irregular threads. Frontal ring convex, not constricted by the equatorial ring. Basal ring with six short conical divergent feet (two sagittal and four lateral). Sagittal ring with an apical horn. (Resembles some Spyroidea.)

Dimensions.—Length of the shell 0.08, breadth 0.12.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

Genus 429. Octotympanum,^[48] n. gen.

Definition.—Tympanida with two bisected horizontal rings converging laterally and connected in the lateral poles of the equatorial plane. Eight large gates.

The genus Octotympanum differs from all other Tympanida in the peculiar connection of the two horizontal rings, which here reach the maximum of their growth, converge towards the equator, and come into direct contact on the poles of the equatorial transverse axis. Therefore the shell appears to be composed of three complete vertical meridian rings, the middle of which (the sagittal ring) is free and simple; the two other (subfrontal) rings are grown together at the lateral poles of the equatorial plane; commonly at these poles there arises (on the right and left) a strong lateral spine, and the base of this (or the crossing point of the two touching horizontal rings) corresponds to the remnants of the shortened frontal ring. The crown-shaped shell exhibits therefore eight large gates; two superior (mitral) and two inferior basal gates, two larger anterior (facial) and two larger posterior (occipital) gates. Seen from the lateral poles only two of the former are visible, and represent the figure of a vertical 8; seen from the sagittal poles, only two of the latter are visible, in the form of a larger horizontal . Octotympanum may be derived from Acrocubus by reduction of the lateral frontal ring to a knot (or cross-point), and by maximal extension of the two parallel horizontal rings, which become curved downwards laterally and touch at the lateral poles.

1. Octotympanum octospinum, n. sp.

Mitral gates smaller than the basal gates; upper halves of the two lateral meridional rings smaller than the lower halves. Rings with few scattered thorns; four larger simple spines, nearly horizontal in the equatorial plane; two on the poles of the sagittal axis, two on the poles of the lateral axis. Four other large spines, nearly vertical at the four lowermost basal points of the subfrontal rings.

Dimensions.—Length of the shell 0.09, breadth 0.12.

Habitat.—Central Pacific, Station 273, depth 2350 fathoms.

2. Octotympanum octonarium, n. sp. (Pl. 94, fig. 3).

Mitral gates of the same size as the basal gates; upper and lower halves of the meridional rings of equal size. Rings armed with numerous stout, thorny, simple and forked spines; four very large branched spines in the equatorial plane, nearly horizontal, two on the poles of the sagittal, two on the poles of the transverse axis, the latter curved downwards.

Dimensions.—Length of the shell 0.1, breadth 0.2.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

3. Octotympanum arborescens, n. sp.

Mitral gates smaller than the basal gates, the lower halves of the lateral rings being broader than the upper halves. Rings very spiny, armed with numerous branched spines; ten very large arborescent spines on the lateral rings; two on the poles of the transverse axis, eight on the prominent corners of the diagonal axes (four upper and four lower); sagittal ring thorny.

Dimensions.—Length of the shell 0.8, breadth 0.16.

Habitat.—Central Pacific, Station 274, depth 2750 fathoms.

4. Octotympanum cervicorne, n. sp. (Pl. 94, fig. 2).

Mitral and basal gates of equal size, the lower and upper halves of the two crossed lateral rings being nearly equal. Rings armed with numerous branched spines; two very large spines, similar to the antlers of a deer, on the poles of the lateral axis; their branches about half as large as the whole shell. Sagittal ring nearly smooth, with few small thorns on the poles of the main axis.

Dimensions.—Length of the shell 0.16, breadth 0.2.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

Genus 430. Tympaniscus,^[49] n. gen.

Definition.—Tympanida with two bisected horizontal rings, which are connected by three vertical meridional rings (or six columellæ).

The genus Tympaniscus and the following Tympanidium differ from all preceding Tympanida in the multiplication of the vertical columellæ, which connect the two horizontal bisected rings. Tympaniscus exhibits six columellæ, which may be regarded as halves of three meridional rings. Only one, however, of these is complete (the sagittal ring, which bisects the mitral and the basal ring); the two other meridional rings (placed in diagonal planes) may be regarded as produced by lateral bifurcation of an incomplete frontal ring; this appears to be already foreshadowed in the preceding Octotympanum.

1. Tympaniscus corona, n. sp.

Basal ring larger than the mitral ring, with numerous irregular short spines but without descending feet. Six columellæ strongly curved, in the lower half thicker and thorny; the four lateral much thinner than the two sagittal. Apex of the jointed sagittal ring with a conical horn.

Dimensions.—Length of the shell 0.08, breadth 0.11.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

2. Tympaniscus bipes, n. sp.

Basal ring of about the same size as the mitral ring, with two lateral descending feet, which are parallel and vertical, simple, without spur, half as long as the sagittal ring. The latter is ovate, twice as long and broad as the two circular frontal rings.

Dimensions.—Breadth of the shell 0.14, length 0.09.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

3. Tympaniscus dipodiscus, n. sp. (Pl. 94, figs. 5, 6).

Basal ring smaller than the mitral ring, with two lateral descending feet, which are nearly parallel and vertical, obtuse, about as long as the sagittal ring, and which bear on the outside a horizontal spur. Sagittal ring hexagonal, very stout, with a caudal appendix at the base, and with a small sagittal arch, bearing a stout spinulate double knob at the apex. The two subfrontal rings depressed, twice as broad as high, on the outside thorny, connected at each side in the lower half by a double transverse arch.

Dimensions.—Breadth of the shell 0.18, length 0.08 (with spines 0.18).

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

4. Tympaniscus tripodiscus, n. sp. (Pl. 94, fig. 7).

Basal ring of about the same size as the mitral ring, with three large and stout divergent feet (two lateral and one caudal). Sagittal ring stout, broader than the two spiny subsagittal rings; the upper part of the latter bears two ascending arches, which are united with the large apical horn arising from the apex of the sagittal ring. Six columellæ nearly vertical, slightly curved on the outside; their lateral edges armed with numerous simple or forked spines.

Dimensions.—Breadth of the shell 0.1, total length 0.12.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

5. Tympaniscus quadrupes, n. sp. (Pl. 94, fig. 4).

Basal ring larger than the mitral ring, with four short vertical three-sided pyramidal feet of equal size (two lateral and two sagittal); the feet are three-sided pyramidal, with finely denticulate median edges, and bear at the base a horizontal thorny spur. Sagittal ring at the apex with a very large cross-shaped horn, bearing two horizontal thorny lateral branches; the horn is supported by an anterior and a posterior arch. Six columellæ strongly curved and dentate.

Dimensions.—Breadth of the shell 0.15, length 0.12.

Habitat.—South Pacific, Station 298, depth 2225 fathoms.

6. Tympaniscus fibula, Haeckel.

Ceratospyris fibula, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx. fig. 3.

Basal ring of about the same size as the mitral ring, with six large conical descending feet; these are prolongations of the six columellæ, nearly of the same length, slightly divergent, and bear at the base a strong horizontal spur. The six columellæ are strongly curved, spiny, and bear above small arches, which are united with the apical horn of the sagittal ring.

Dimensions.—Breadth of the shell 0.09, height 0.05; total height 0.09.

Habitat.—Fossil in Barbados.

7. Tympaniscus dodecaster, n. sp.

Basal ring of the same size as the mitral ring, with six very large and six alternating smaller, slightly divergent, curved feet, about as long an the shell; the larger are the basal prolongations of the six curved, thorny columellæ. Mitral ring spiny, not overgrown with arches, as in the similar preceding species.

Dimensions.—Length of the shell 0.08, breadth 0.12.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

Genus 431. Tympanidium,^[50] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two bisected horizontal rings, which are connected by four vertical meridional rings (or eight columellæ).

The genus Tympanidium differs from all other Protympanida in the development of four vertical rings, placed in four different meridional planes. Only one of these is complete, the primary sagittal ring; the three others are incomplete, inserted on the two horizontal rings, which are formed by the paired mitral and basal branches of the sagittal ring; one of these three lies in the frontal plane, the two others in diagonal meridional planes (between the frontal and sagittal). The shell therefore exhibits twelve large gates, four of which are horizontal (the two superior mitral and the two inferior basal gates); the eight others are vertical, separated by the eight columellæ, or the halves of the four meridional rings. In the subgenus Tympanomma the number of gates amounts to sixteen, the four lateral gates being bisected by an incomplete equatorial ring. The genus Tympanidium may be derived from Acrocubus by development of the two diagonal rings (between the frontal and sagittal).

Subgenus 1. Tympanura, Haeckel.

Definition.—Shell with twelve gates; the four lateral gates simple.

1. Tympanidium foliosum, n. sp. (Pl. 94, fig. 1).

Shell with twelve gates; the four lateral gates simple. Basal gates of the shell larger than the mitral gates. Sagittal ring ovate, much smaller than the three other meridional rings, which are armed with numerous large elegant spines, bearing a lanceolate leaf on a thin pedicle. The sagittal ring bears a bunch of similar spines only at the apex, and on both poles of the sagittal axis (in the equator) a single forked spine, with two thorny branches.

Dimensions.—Length of the shell 0.09 (with spines 0.25), breadth 0.15.

Habitat.—South Pacific, Station 300, depth 1375 fathoms.

2. Tympanidium spinosum, n. sp.

Shell with twelve gates; the four lateral gates simple. Basal and mitral gates of about equal size. Shell similar to that of the preceding species, differing mainly in the different armature; the numerous spines, covering the convex outside of the four vertical rings, are not leaf-shaped, but conical, short, of very variable size, partly simple, partly irregularly branched.

Dimensions.—Length of the shell 0.08 (with spines 0.2), breadth 0.12.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

Subgenus 2. Tympanomma, Haeckel.

Definition.—Shell with sixteen gates (eight median gates, paired on both sides of the sagittal ring, and eight lateral gates, paired on both sides of the frontal ring). The four lateral gates of the two preceding species (subgenus Tympanura) are bisected in Tympanomma by the lateral parts of an incomplete equatorial ring.

3. Tympanidium binoctonum, n. sp. (Pl. 94, fig. 18).

Shell with sixteen gates; the four lateral gates double, bisected by the lateral parts of an incomplete equatorial ring. Basal gates nearly rectangular, of the same breadth as the pentagonal mitral gates, but twice as long. Equatorial outline of the shell (seen in fig. 18 from the apical pole) octagonal. All rods of the shell thin, smooth.

Dimensions.—Transverse axis of the shell 0.1, sagittal axis 0.06.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

4. Tympanidium barbadense, Haeckel.

"Hollow cylinder," &c., Bury, 1862, Polycystins of Barbados, pl. xvi. fig. 1.

Shell with sixteen gates; the four lateral gates double, bisected by an incomplete equatorial ring. Basal gates kidney-shaped, of the same breadth as the circular mitral gates, but twice as long. Equatorial outline of the shell elliptical. All rods of the shell thin, smooth.

Dimensions.—Transverse axis of the shell 0.12, sagittal axis 0.08.

Habitat.—Fossil in South Naparima, Trinidad, Barbados.

5. Tympanidium staurocircum, n. sp.

Shell with sixteen gates; the four lateral gates double, bisected by an incomplete equatorial ring. Basal and mitral gates of the shell of about equal size, roundish. Equatorial outline of the shell violin-shaped, with a sagittal constriction. All rods of the shell armed with short irregular spines.

Dimensions.—Transverse axis of the shell 0.12, sagittal axis 0.06.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

Subfamily 2. Paratympanida, Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two fenestrated horizontal rings, which are connected by a variable number of vertical rods or columellæ. The shell therefore becomes more completely latticed than in the other Tympanida, and approaches that of the Spyroidea.

Genus 432. Paratympanum,^[51] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two latticed horizontal rings, connected by numerous descending and diverging columellæ; mitral ring smaller than the basal ring.

The genus Paratympanum and the following nearly allied Lithotympanum form together the small subfamily of Paratympanida, distinguished from the other Tympanida by the fenestration of the two parallel horizontal rings. These rings in Lithotympanum are both equal, whilst in Paratympanum, the basal ring is larger than the mitral ring; therefore the connecting rods or columellæ are in the former parallel and vertical, in the latter divergent and descending. Two opposite ones of these columellæ are parts of the primary sagittal ring, two others are parts of the lateral or frontal ring, whilst the remainder are afterwards intercalated. Paratympanum may be derived from Dystympanium by fenestration of the basal ring.

1. Paratympanum hexastylum, n. sp.

Six divergent columellæ, about as long as the diameter of the hexagonal mitral ring, connect it with the larger hexagonal basal ring. Lattice of the mitral ring hemispherical, with six roundish pores, surrounding a central apical horn. Lattice of the basal ring with one large central pore, surrounded by numerous peripheral pores. Rings and rods smooth, without spines.

Dimensions.—Length of the shell 0.07; breadth of the mitral ring 0.06, of the basal ring 0.09.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

2. Paratympanum octostylum, n. sp. (Pl. 94, fig. 14).

Eight divergent columellæ, about as long as the diameter of the octagonal mitral ring, connect it with the larger circular basal ring, and bear at each end a divergent, strong, conical spine. Lattice-plate of both rings slightly convex, with numerous subregular circular pores, smooth, without surface spines.

Dimensions.—Breadth of the mitral ring 0.06, of the basal ring 0.09.

Habitat.—Central Pacific, Station 268, depth 2900 fathoms.

3. Paratympanum decastylum, n. sp.

Ten divergent columellæ, only half as long as the diameter of the decagonal mitral ring, connect it with the larger circular basal ring. Lattice-plate of the mitral ring nearly hemispherical of the basal ring flat, both with numerous irregular roundish pores and scattered spines. Margin of both rings spiny.

Dimensions.—Breadth of the mitral ring 0.08, of the basal ring 0.1.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Genus 433. Lithotympanum,^[52] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two latticed horizontal rings, connected by numerous parallel and vertical columellæ; mitral and basal rings of equal size.

The genus Lithotympanum has the form of a cylindrical drum, the two fundamental faces of which (the mitral and basal gates) are closed by lattice-work. Both horizontal rings are equal, whilst in the preceding Paratympanum the basal gate is larger than the mitral. It may be derived from the latter by equalisation of these two rings, or directly from Dystympanium by fenestration of the basal ring.

1. Lithotympanum tuberosum, n. sp. (Pl. 83, fig. 1).

Both lattice-plates slightly convex; the mitral plate with six larger marginal pores and one central pore separated by numerous smaller pores; the basal plate with seven large pores only (one central and six peripheral). Surface and margin of the plates uneven, with roundish prominent dimpled tubercles. Both rings connected by ten to twelve simple cylindrical vertical columellæ.

Dimensions.—Length of the shell 0.13, breadth 0.1.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

2. Lithotympanum spinosum, n. sp.

Both lattice-plates flat, with numerous irregular roundish pores of variable size. Surface thorny. Margin with numerous irregular spines, directed upwards on the mitral, downwards on the basal plate. Both rings connected by eight simple cylindrical vertical columellæ.

Dimensions.—Length of the shell 0.12, breadth 0.08.

Habitat.—Western Tropical Pacific, Station 224, depth 1850 fathoms.

Subfamily 3. Dystympanida, Haeckel.

Definition.—Tympanida with fenestrated mitral ring and simple open basal ring; both horizontal rings connected by numerous vertical or divergent columellæ.

Genus 434. Dystympanium,^[53] n. gen.

Definition.—Tympanida with two horizontal rings, connected by numerous (six to eight or more) divergent columellæ. The upper mitral ring is smaller and latticed, the lower basal ring larger and open.

The genus Dystympanium, representing a peculiar subfamily, differs from all other Tympanida in the different shape of the two parallel horizontal rings. The upper or mitral ring is closed by a lattice-plate (as in Paratympanum), the lower or basal ring is simple and open (as in Eutympanium). Dystympanium may therefore be regarded as an intermediate form between these two genera, and may perhaps be derived from Paratympanum by loss of the lower lattice-plate.

1. Dystympanium dictyocha, n. sp. (Pl. 94, figs. 15, 16).

Basal ring circular, with eighteen to twenty short conical divergent spines. Mitral ring about two-thirds as broad, hexagonal, with six ascending spines on the six corners. The latter are connected with the former by six simple, straight, obliquely descending columellæ, about as long as the diameter of the mitral ring. Mitral lattice-plate slightly convex, with seven roundish pores (six peripheral pores around a central pore).

Dimensions.—Diameter of the basal ring 0.09, mitral ring 0.06; length of the columellæ 0.05.

Habitat.—Tropical Atlantic, Station 338, depth 1990 fathoms.

2. Dystympanium distephanus, n. sp.

Basal ring hexagonal, with six larger spines at the six corners, and numerous smaller ones between them. Mitral ring half as broad as the basal ring, also with six angular spines. The latter are connected with the former by six divergent curved columellæ, about as long as the diameter of the basal ring. Mitral lattice-plate flat, with irregular roundish pores.

Dimensions.—Diameter of the basal ring 0.1, mitral ring 0.05; length of the columellæ 0.09.

Habitat.—Equatorial Atlantic, Station 347, depth 2250 fathoms.

3. Dystympanium medusa, n. sp.

Basal ring circular, with eight larger and numerous smaller divergent spines. Mitral ring two-thirds as broad as the basal ring, octagonal, with eight conical ascending spines on the eight corners. The latter are connected with the former by eight divergent, curved columellæ, as long as the diameter of the mitral ring. Mitral lattice-plate nearly hemispherical, with nine circular pores (eight peripheral pores around one central pore).

Dimensions.—Diameter of the basal ring 0.12, mitral ring 0.08; length of the columellæ 0.09.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Subfamily 4. Eutympanida, Haeckel.

Definition.—Tympanida with two simple horizontal rings, which are connected by a variable number of vertical rods or columellæ. Therefore the shell exhibits a large simple mitral gate on the upper, and a large simple basal gate on the lower side; between the two a variable number of lateral gates.

Genus 435. Parastephanus, Haeckel, 1881, Prodromus, p. 446.

Definition.—Tympanida with two simple horizontal rings, connected by two vertical columellæ.

The genus Parastephanus is the simplest among the Eutympanida, and exhibits only two vertical rods or columellæ, which connect the two parallel horizontal rings. One of these latter must be regarded as the mitral or superior ring, the other as the basal or inferior ring; whilst the two parallel columellæ, connecting both, are the remaining vertical parts of the sagittal ring, the upper and lower parts of which are lost. By loss of the latter Parastephanus has probably been derived from Protympanium.

1. Parastephanus circularis, n. sp.

Two horizontal rings smooth, circular, of equal size, connected by two curved smooth columellæ, which are somewhat shorter than the diameter of the rings.

Dimensions.—Diameter of the rings 0.08, length of the columellæ 0.06.

Habitat.—Central Pacific, Station 263, depth 2650 fathoms.

2. Parastephanus quadrispinus, n. sp. (Pl. 93, fig. 21).

Two horizontal rings smooth, elliptical or nearly circular, of equal size, connected by two vertical, slightly curved columellæ, which are about as long as the radius of the rings. Each ring bears two simple lateral spines, which in the mitral ring are curved downwards, in the basal ring upwards, possibly the last remains of a reduced frontal ring.

Dimensions.—Diameter of the rings 0.09, length of the columellæ 0.05.

Habitat.—North Pacific, Station 236, surface.

3. Parastephanus asymmetricus, n. sp. (Pl. 82, fig. 10).

Two horizontal rings thorny, of equal size, irregularly ovate or nearly semicircular, and of somewhat asymmetrical form. The two connecting parallel columellæ are straight, cylindrical, about as long as the diameter of the rings. The peculiar asymmetry in the form of the rings raises the possibility that the two columellæ in this species are the remaining parts of a frontal ring, and that the sagittal ring has altogether disappeared. In this case the convex half of both rings would be the ventral, the straight half the dorsal part.

Dimensions.—Diameter of the rings 0.1, length of the columellæ 0.08.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

4. Parastephanus dispar, n. sp.

Two horizontal rings elliptical, thorny, of different sizes, the basal ring one and a half times as broad as the mitral ring. The two connecting columellæ are curved, somewhat longer than the diameter of the mitral ring.

Dimensions.—Diameter of the basal ring 0.09, mitral 0.06; length of the columellæ 0.07.

Habitat.—South Pacific, Station 300, depth 1375 fathoms.

Genus 436. Prismatium,^[54] Haeckel, 1862, Monogr. d. Radiol., p. 270.

Definition.—Tympanida with two simple horizontal rings, connected by three vertical columellæ.

The genus Prismatium was hitherto the only known form of the Tympanida, and the only species described in 1862 in my Monograph was Prismatium tripleurum (loc. cit., p. 270, pl. iv. fig. 6). A new species from the Challenger collection (Pl. 93, fig. 22), Prismatium tripodium, explains the true structure of this remarkable genus. The skeleton is composed of nine siliceous rods, corresponding to the edges of a trilateral prism. Six of these are horizontal, and enclose the two parallel triangular horizontal gates, the superior of which is formed by the mitral or coryphal, and the inferior by the basal or cortinar ring. The three other rods are vertical and nearly parallel, and connect (as lateral edges of the prism) the corresponding corners of the two parallel horizontal triangles. Two of these vertical columellæ, together with the two horizontal parallel rods connecting them, represent the complete frontal ring, whilst the third vertical columella is the posterior half of the sagittal ring, the other parts of which are lost.

1. Prismatium tripodium, n. sp. (Pl. 93, fig. 22).

Mitral ring triangular, somewhat smaller than the triangular basal ring, both connected at the corners by three vertical, slightly curved columellæ. From the six corners arise six radial spines of different size and form; the two paired spines of the mitral ring are simple and very small, whilst those of the basal ring are three times as long and bear a lateral branch. The odd spine of the third corner is on both rings larger, and distinguished by some thorns. This difference seems to indicate that these two odd spines correspond to the apical horn and the caudal foot of Cortina, and the columella between them is the rest of the reduced sagittal ring. In this case the quadrangular vertical ring, which is composed of the two paired columellæ and the two connecting horizontal rods, would be probably the frontal ring.

Dimensions.—Length of the shell 0.09, breadth 0.07.

Habitat.—Equatorial Atlantic, Station 347, surface.

2. Prismatium tripleurum, Haeckel.

Prismatium tripleurum, Haeckel, 1862, Monogr. d. Radiol., p. 270, Taf. iv. fig. 6.

Acanthodesmia prismatium, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 799.

Mitral and basal rings of equal size, equilateral triangular, both connected at the corners by three vertical equal columellæ. From the six corners arise six short, equal, conical radial spines. The nine rods of the shell correspond to the nine edges of a triangular equilateral prism.

Dimensions.—Length of the shell 0.044, breadth 0.032.

Habitat.—Mediterranean (Messina), surface.

Genus 437. Pseudocubus,^[55] n. gen.

Definition.—Tympanida with two simple horizontal rings of different sizes, connected by four divergent columellæ.

The genus Pseudocubus exhibits the characteristic form of an obelisk, or a truncated four-sided pyramid. The four edges of this obelisk, or the four "columellæ," are the remaining parts of the two incomplete vertical rings; two opposite edges are the dorsal and ventral rod of the sagittal ring; the two alternate edges between these are the lateral rods of the frontal ring. The two horizontal rings, which become connected by the four divergent columellæ, are the smaller mitral ring and the larger basal ring; both are either square or nearly circular.

1. Pseudocubus obeliscus, n. sp. (Pl. 94, fig. 11).

Mitral ring square, with circular gate and two divergent simple spines on each corner. Basal ring twice as broad, square, with four convex sides and one simple spine on each corner. Four columellæ straight. All twelve rods with three smooth edges.

Dimensions.—Breadth of the mitral ring 0.02, of the basal ring 0.05.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

2. Pseudocubus octostylus, n. sp.

Mitral ring square, with one stout pyramidal spine on each corner. Basal ring twice as broad, square, also with a single strong spine on each corner. Four columellæ straight. All twelve rods with three smooth edges.

Dimensions.—Breadth of the mitral ring 0.04, of the basal ring 0.08.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

3. Pseudocubus hexapylus, n. sp. (Pl. 94, fig. 12).

Mitral ring circular, two-thirds as broad as the subcircular, or nearly square, basal ring; both rings with a simple spine on the two sagittal corners (dorsal and ventral), with a forked or branched larger spine on the two lateral corners (right and left). All twelve rods more or less curved and thorny.

Dimensions.—Breadth of the mitral ring 0.07, of the basal ring 0.1.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

Genus 438. Lithocubus,^[56] Haeckel, 1881, Prodromus, p. 447.

Definition.—Tympanida with two simple horizontal rings of equal size, connected by four parallel vertical columellæ.

The genus Lithocubus is very remarkable for the regular cubical form of the skeleton, which is composed of twelve siliceous rods, corresponding to the twelve edges of a cube. Eight of these are horizontal, and enclose the two parallel square horizontal gates, the superior mitral and the inferior basal gate. The four other rods are vertical, parallel, and connect (as lateral edges of the cube) the corresponding corners of the two horizontal squares. Two opposite ones of these four vertical columellæ are the remaining halves of the incomplete sagittal ring; the two alternate are the remaining halves of the incomplete frontal ring. The four lateral gates between these four columellæ are also square or rectangular, and either of the same size as the two horizontal gates, or somewhat larger. Lithocubus may be derived from Acrocubus by reduction of the coryphal and the basal part of the primary sagittal ring, the only remaining parts of which are the anterior and the posterior columellæ.

1. Lithocubus geometricus, n. sp. (Pl. 94, fig. 13).

The twelve rods, corresponding to the edges of the geometrical cube, are straight and smooth; the eight corners provided with a small conical thorn. The shell exhibits six equal square sides, and represents therefore exactly the geometrical form of a cube.

Dimensions.—Diameter of the cube 0.05; thickness of the bars 0.008.

Habitat.—Tropical Pacific, Station 224, depth 1850 fathoms.

2. Lithocubus octacanthus, n. sp.

The twelve rods of the cubical shell are slightly curved, convex, smooth, as in the similar preceding species. It differs from that in the development of eight slender radial spines, arising from the eight corners of the geometrical cube, from two to three times as long as its diameter, and lying opposite in pairs in its diagonals.

Dimensions.—Diameter of the cube 0.06; length of the spines 0.15.

Habitat.—North Atlantic, Canary Islands, surface.

3. Lithocubus vinculatus, Haeckel.

Acanthodesmia vinculata, J. Müller, 1856 (partim), Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. i. fig. 7 (not 4-6).

The twelve rods of the cubical shell are curved and armed with scattered, simple, short spines. The figure 7 of Johannes Müller (loc. cit.) corresponds exactly to the Mediterranean form observed by me at Portofino, and is quite different from his true Acanthodesmia vinculata (loc. cit., figs. 4-6), so that I have no doubt he did observe these two different species (compare above, p. 975).

Dimensions.—Diameter of the cube 0.07; length of the spines 0.02.

Habitat.—Mediterranean (Nice, Portofino).

4. Lithocubus astragalus, n. sp. (Pl. 82, fig. 12).

The twelve rods of the cubical shell are stout and slightly curved, armed with numerous, simple, and irregularly branched spines. Eight larger spines, branched like a deer's antler, arise from the eight corners of the cube.

Dimensions.—Diameter of the cube 0.1 to 0.12; length of the corner spines 0.05 to 0.08.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Genus 439. Circotympanum,^[57] n. gen.

Definition.—Tympanida with two simple different horizontal rings, connected by numerous (six to eight or more) divergent columellæ.