Legion III. NASSELLARIA, (continued 2)

Dimensions.—Length of the spines 0.2, of the middle rod 0.01.

Habitat.—Central Pacific, Station 266, surface.

Subfamily 4. Polyplectida, Haeckel, 1881, Prodromus, p. 424.

Definition.—Plectanida with numerous (seven to nine or more) radial spines.

Genus 400. Polyplecta,^[19] Haeckel.

Definition.—Plectanida with numerous (seven to nine or more) radial spines, arising from a common centre and lying in different planes.

The genus Polyplecta comprises provisionally all Plectanida possessing seven or more radial spines, united in the centre of the framework. It may be derived from Polyplagia by meeting and concrescence of the free branches. But as in the latter genus, here also the few observed species are very different, perhaps of different origin, and may be afterwards better separated as representatives of diverse genera.

1. Polyplecta heptacantha, n. sp. (Pl. 91, fig. 12).

Heptaplegma heptacantha, Haeckel, 1882, MS.

Seven unequal spines divergent from one common central point, slender, slightly curved, three-sided prismatic. Four spines are much larger, twice to three times as long and as thick as the three smaller spines. One of the four larger spines is directed upwards (as "apical horn"), whilst the three others diverge downwards (as "basal feet"). Each of the four larger spines bears five to seven equidistant verticils of three divergent branches, the proximal of which are branched, the distal simple. The three smaller spines lie nearly horizontally, midway between the odd apical spine and the three basal spines, and in the same meridian planes with them; each bears one verticil of three divergent branches. All the branches are united by arachnoidal threads, composing a loose wickerwork with irregular, generally quadrangular meshes.

Dimensions.—Length of the four larger spines 0.27 to 0.33, of the four smaller 0.1 to 0.14.

Habitat.—Central Pacific, Station 271, surface.

2. Polyplecta enneacantha, n. sp.

Enneaplegma enneacantha, Haeckel, 1881, Prodromus, p. 425.

Nine equal and equidistant, straight, cylindrical radial spines, lying nearly in one plane, arise from an irregular spongy central framework; six of them seem to be secondary, intercalated between three equidistant primary spines, which are united in the centre. (This species resembles in the nine-radial structure the remarkable Enneaphormis rotula, Pl. 57, fig. 9, and may perhaps be derived from a similar species; but it has no regular latticed shell.)

Dimensions.—Length of the spines 0.22, diameter of the framework 0.17.

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

3. Polyplecta decacantha, n. sp.

Pentaplegma decacantha, Haeckel, Prodromus, p. 425.

Ten radial spines, curved, cylindrical, irregularly branched, diverge in different directions and seem to arise in pairs from an irregular central framework, in the centre of which five primary spines are united; the latter correspond probably to the five spines of Pentaspyris, &c. The density of the spongy central framework did not allow of an accurate investigation, and makes it doubtful whether this species is not a Spongiomma.

Dimensions.—Length of the spines 0.3 to 0.4, diameter of the framework 0.18.

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

4. Polyplecta polybrocha, Haeckel.

? Acanthodesmia polybrocha, Haeckel, 1865, Zeitschr. f. wiss. Zool., Bd. xv. p. 368, Taf. xxvi. fig. 3.

Plegmosphæra polybrocha, Haeckel, 1881, Prodromus, p. 455.

Numerous (twenty to thirty or more) radial spines, thin, cylindrical, curved and irregularly branched, arising from an irregular central spongy framework, are connected by numerous slender arches. The specimen observed by me in 1880 in Portofino was a true Polyplecta, with three primary spines centrally united, between which numerous other spines were intercalated. The similar specimen, however, observed in 1864 in Villafranca, and figured, loc. cit., was perhaps a Plegmosphæra.

Dimensions.—Length of the radial spines 0.05 to 0.1, diameter of the framework 0.16.

Habitat.—Mediterranean (Villafranca, Portofino), surface.

5. Polyplecta dumetum, Haeckel.

Acanthodesmia dumetum, J. Müller, 1868, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 30, Taf. i. Fig. 3.

Numerous (ten to twelve or more) radial spines, thin and straight, with a few straight lateral branches, diverge in different directions and are connected by a few slender curved arches. Some similar forms, but more developed, with numerous branches and curved rods, are found in the Pacific Radiolarian ooze, and represent probably different species.

Dimensions.—Length of the radial spines 0.05 to 0.08, of the branches 0.02 to 0.03.

Habitat.—Mediterranean, French shore (Cette and Saint Tropez), Johannes Müller, surface.

Suborder III. STEPHOIDEA, Haeckel.

Definition.—Nassellaria without complete lattice-shell, with a skeleton composed of one or more simple rings, which may be united by a loose framework and are separated by large openings or gates. One primary or sagittal ring, determining the sagittal or median plane of the bilateral body, encloses the monaxonian central capsule.

The suborder Stephoidea, hitherto known by a few species only of "Acanthodesmida," comprises a large number of interesting Nassellaria (now more than two hundred species), which possess peculiar interest for the morphology and phylogeny of this legion. The monaxonian central capsule of the Stephoidea is surrounded either by one simple ring or by a complex system of several loosely connected rings; these may be united by a loose framework of connected branches, but never produce a complete lattice-shell, as is constantly the case in the Spyroidea, Botryodea, and Cyrtoidea. Therefore there remain between the parts of the connected rings a few large openings which we call "gates," separating them from the numerous small "pores" of the complete lattice-shells. In the most simple case, if only one ring be formed, there is also present only one "gate," the aperture of this simple ring.

The first known species of Stephoidea were observed in the Mediterranean by Johannes Müller in 1856, and described and figured in his last treatise (1858) under the names Lithocircus annularis (loc. cit., Taf. i. fig. 1) and Acanthodesmia vinculata (loc. cit., Taf. i. figs. 4-7). In the following year I myself observed two other living species in the Mediterranean, and described them in my Monograph (1862, pp. 268, 270) as Zygostephanus mülleri (Taf. xii. fig. 2) and Prismatium tripleurum (Taf. iv. fig. 6). For these four longest known Stephoidea I founded the new family of Acanthodesmida (loc. cit., p. 265), but united with them two other similar genera which I afterwards separated:—Plagiacantha (belonging to the Plectoidea) and Dictyocha (belonging to the Phæodaria).

When, in 1876, I received the rich material of the Challenger collection, I was astonished to find in it an enormous number of new, similar, and partly very interesting "Acanthodesmida," which were afterwards arranged in my Prodromus (1881, p. 444) in thirty-eight different genera and four "subfamilies," all united in one single large family, "Stephida or Monopylaria cricoidea." I retain here this natural group in the same sense, but give to it the rank of a "suborder," separating at the same time its four subfamilies as substantial "families." Since the names of the latter, proposed in the Prodromus, were not quite suitable, I replace them here by the following more convenient names:—

1. Family Stephanida (= Monostephida, 1881, p. 447). Skeleton entirely formed by one simple ring (the primary vertical sagittal ring). The only "gate" is the simple aperture of the ring.

2. Family Semantida (= Dyostephida, 1881, p. 446). Skeleton composed of two rings, perpendicular to one another; the primary vertical sagittal ring bears at the base a horizontal basal ring; between the two rings two or more "basal gates remain."

3. Family Coronida (= Triostephida, 1881, p. 445). Skeleton composed of two crossed vertical or meridional rings, perpendicular to one another—the primary sagittal ring and the secondary frontal ring. Commonly the two vertical rings are united at the base by a horizontal basal ring, and between them remain two or more "basal gates."

4. Family Tympanida (= Parastephida, 1881, p. 446). Skeleton composed of two parallel horizontal rings, and upper mitral ring, and a lower basal ring, both connected by vertical or divergent columellæ, which are parts of vertical rings (primary sagittal, and secondary frontal ring).

The peculiar structure of the central capsule of the Stephoidea, and their character as true Monopylea, were first recognised by Richard Hertwig, who in 1879, in his Organismus der Radiolarien, gave an excellent detailed description of it (loc. cit., pp. 68-72, Taf. vii. figs. 4, 5). He also pointed out the near affinity of these "Acanthodesmida" with the Spyroidea or Zygocyrtida, uniting the latter with the former family.

A fuller explanation of this affinity, and of the morphological and phylogenetic importance of the "Acanthodesmida," as ancestral forms of the Spyroidea and Cyrtoidea, was given in 1882 by Bütschli (Zeitschr. f. wiss. Zool., vol. xxxvi. pp. 495-501). He described in detail some important fossil forms of Acanthodesmida as different species of "Stephanolithis," a name which Ehrenberg had employed for various ring-like fragments of Radiolarian shells, sponges, and other fossil bodies. The four fossil species which Bütschli described represent four different genera of Stephoidea, viz., Semantis (spinescens), Semantrum (mülleri), Semantidium (haeckelii), and Tristephanium (hertwigii). On the phylogenetic conclusions, derived from these accurate observations, compare above, p. 893, &c. The topographical signification of the parts, employed by Bütschli, is contrary to mine; he calls my dorsal side the "anterior," and my ventral side the "posterior."

The geometrical fundamental form of the body in nearly all Stephoidea (with few exceptions) is distinctly bilateral or "dipleuric," so that we can easily distinguish the three different dimensive axes: the principal axis with different apical and basal poles, the sagittal axis with different dorsal and ventral poles, and the lateral axis with equivalent right and left poles. In only a few genera this bilateral symmetry is not expressed, and a simpler, more regular fundamental form appears. The latter may be either primary (in the monaxonian Archicircus and Lithocircus) or secondary, afterwards acquired (in the octahedral Trissocircus and Trissocyclus, the cubical Lithocubus, the prismatic Eutympanium, and some other forms).

The most important element of the skeleton, with which the formation begins, in all Stephoidea is the simple primary or sagittal ring, lying vertically in the sagittal or median plane of the body and surrounding the monaxonian central capsule. This sagittal ring is the only essential element of the skeleton in all Stephanida, and is completely preserved in all Semantida, also in the greater part of the Coronida and Tympanida. It is partially reduced in the small groups of the true Acanthodesmida (subfamily of Coronida) and the Dystympanida and Eutympanida (subfamilies of Tympanida). Here only the vertical parts of it are preserved (dorsal and ventral rod), whilst the horizontal parts are lost (mitral and basal rod).

The sagittal ring lies constantly in the vertical median plane of the body, and therefore divides the enclosed central capsule into a right and a left half. It is rarely regular or subregular, commonly dipleuric or distinctly bilateral, so that we may easily distinguish its dorsal and ventral, apical and basal parts. The most important of these four parts or "rods" is the "basal rod" or the inferior part, because here the ring is in closer connection with the central capsule and its "porous area"; here peculiar spines or branches are commonly developed, which even on the isolated ring immediately determine the basal pole. The opposite upper part, or the "mitral rod," is also often distinguished by the peculiar appendages. The posterior part, or the "dorsal rod" (the anterior rod, a, in the description of Bütschli), is commonly more straight, often quite vertical. The opposite anterior part, or the "ventral rod" (the posterior rod, b, of Bütschli), is usually more convex, and often strongly curved or semicircular.

Whilst this dipleuric or bilateral (commonly obliquely ovate or nearly triangular) form of the sagittal ring is distinctly preserved in by far the greater number of Stephoidea, it is replaced in some few genera by a more regular, amphithect, diphragmatic, or biradial form. In this case we may often suppose a primary regularity to exist, the dorsal and ventral parts being not yet differentiated, as in Archicircus and Lithocircus, Zygostephanus and Protympanium, and perhaps also in some other forms. But in other cases the regularity is, on the contrary, secondary, being derived from original bilateral forms.

The rod of the sagittal ring is either cylindrical (with circular transverse section) or angular (commonly with triangular transverse section). In nearly all Stephoidea (with very few exceptions) branches or apophyses are developed from the ring, regularly disposed and often of great morphological importance. Commonly these apophyses are developed in pairs, growing symmetrically on both sides of the ring. The most important of these apophyses are:—(1) Basal apophyses, arising from the basal hole of the ring; (2) mitral apophyses, arising from the apical pole; (3) dorsal apophyses, arising from the middle of the dorsal rod; and (4) ventral apophyses, arising from the middle of the ventral rod. The two former arise in the principal axis, the two latter in the sagittal axis of the body. Very frequently the latter pair is replaced by two pairs of transverse branches, one inferior (mandibular) and one superior (orbital). The apophyses of the ring are either simple or branched, often very large, richly ramified, and give origin to a number of further products.

Whilst in the Stephanida the primary sagittal ring alone represents the whole skeleton, it produces in all other Stephoidea one or more secondary rings. The most important of these is the horizontal basal ring, appearing first in the Semantida (Pl. 92). From the base of the sagittal ring there arise in the horizontal basal plane two pairs of lateral branches or "basal apophyses." The curved opposite branches of the corresponding pairs become united on each side of the primary ring (right and left), and so produce a second, horizontal ring, perpendicular to the former. This basal ring encloses two paired basal gates, which are enclosed on the medial side by the basal rod of the sagittal ring, and on the lateral side by two united apophyses (Semantis, Pl. 92, figs. 1, 2). These two primary basal gates are of the greatest morphological importance; we call them the "jugular gates or jugular pores" (in the description of Bütschli, the pores I, loc. cit., p. 498). The dorsal pair of basal apophyses (on their posterior edge) are the coracal rods, e (rods e of Bütschli); the opposite ventral pair (on their anterior edge) are the clavicular or furcular rods, f (rods e1 of Bütschli); compare Pls. 92-95, and their explanation.

The skeleton of Semantis, the prototype of the Semantida, thus assumes the characteristic form of a signet-ring. The basal ring enclosing the two jugular pores corresponds to the seal-plate. It is commonly more or less horizontal; but often the apophyses descend obliquely (Pl. 92, figs. 1, 2, 13, &c.), more rarely laterally (Pl. 29, fig. 11). The further development of this typical form is essentially effected by the production of new basal pores in the horizontal seal-plate. In Semantrum (Pl. 92, figs. 3, 4, 5) we find already four basal gates. Behind the jugular gates is formed a second pair, the "cardinal gates" (pores II of Bütschli). These are enclosed on the anterior margin by the coracal rods (e), on the posterior margin by the scapular rods (d), a third pair of basal apophyses, arising behind the former from the sagittal ring and uniting with them (the rods e2 of Bütschli). Commonly the two posterior, or cardinal gates are much larger than the two anterior, jugular gates. This characteristic basal plate of Semantrum, with two pairs of basal pores, is of the greatest morphological importance, as it is inherited in by far the greater number of the Nassellaria, though not so generally as Bütschli supposes. The basal ring of Semantrum is either more circular or elliptical, or more polygonal, and is connected with the basal rod of the sagittal ring by three pairs of radial apophyses, the anterior furcular, the middle coracal, and the posterior scapular rods.

A third important form of Semantida is Semantidium (Pl. 92, figs. 6, 7). Here we find three pairs of basal pores in the seal-plate; the third pair, newly formed, consists of the cervical gates (e), bounded in front by the scapular rods (d), behind by a fourth pair of basal apophyses, the cervical rods.

The basal apophyses of the sagittal ring are not only of great morphological importance, because they produce by their union three typical pairs of basal gates or "collar pores," but also because their prolongations often appear as typical basal feet. The distal prolongations of the coracal rods appear in Semantiscus (Pl. 92, figs. 16-18) as two pectoral feet, those of the scapular rods as two tergal feet, whilst the opposite prolongations of the basal rod of the sagittal ring appear as two "sagittal feet" (in front an anterior or sternal, and behind a posterior or caudal foot). In the typical Cortiniscus (Pl. 92, figs. 11-13) only three feet are developed; an odd caudal and two paired pectoral feet (compare above, p. 891). The typical basal ring of the Semantida, with its paired basal gates (Semantis), reappears in the majority of the Coronida, differing from the former in the development of a second vertical ring, which lies in the frontal plane (perpendicular to the sagittal ring), and which we therefore call the frontal ring. In only one small group of the Coronida the basal ring is absent, namely, in the Zygostephanida, and here the frontal ring appears in the simplest form, as a complete elliptical meridian ring, crossing the sagittal ring perpendicularly on the two poles of the main axis (Zygostephanus, Pl. 93, figs. 1-4), Four large lateral gates between the two rings remain open. This form may be derived directly from the Stephanida in the following way; from both poles of a simple sagittal ring there arise two opposite lateral apophyses, which in the frontal plane become curved one towards the other, and united in the poles of the transverse axis. The basal apophyses would be the coracal rods. But it is also possible that Zygostephanus was derived from Semantis by the loss of the furcular rods.

The three typical rings (or the "dimensive rings") of the Stephoidea appear in their most complete form in the subfamily Trissocyclida (Pl. 93, figs. 7, 13). Here all three rings are undivided and completely developed in the three dimensive planes, perpendicular one to another. Between them there remain eight large open gates; the four superior are the four "lateral gates" of Zygostephanus, the four inferior are the four basal gates of Semantrum. The four latter are originally much smaller than the four former; but in Trissocircus and Trissocyclus (Pl. 93, figs. 10-12) they reach the same size. Therefore all eight gates are here of equal form and similar size, and the basal ring, now a true equatorial ring, divides the two meridional rings into two equal halves.

In the Eucoronida, a third subfamily of Coronida, the sagittal and the basal rings are complete, but the frontal ring is incomplete, its basal part being wanting (Pl. 82, figs. 4-6). Therefore we find here six large gates between the three rings; four upper lateral gates (between the two crossed vertical rings) and two lower basal gates (between the basal rod of the sagittal ring and the two halves of the basal ring). Eucoronis, the type of this subfamily, may be derived either directly from Semantis by development of a frontal ring, or from Tristephanium by loss of the basal part of the frontal ring.

A quite simple basal ring with a single gate, distinguishes the fourth subfamily of Coronida, the Acanthodesmida (sensu restricto), the genera Coronidium (Pl. 82, figs. 1, 2, 7, 8) and Acanthodesmia (Pl. 93, fig. 5). The horizontal basal ring alone is here complete, whilst both vertical rings (the sagittal and frontal rings) are incomplete, their basal parts being wanting. Therefore there are here five gates, four lateral and one basal. These forms may be derived from Eucoronis by loss of the basal rod of the primary sagittal ring.

The Tympanida, the fourth family of Stephoidea, exhibit another type of ring structure. Here two parallel horizontal rings are constantly developed, one on the apical pole, the other on the basal pole of the sagittal ring. The latter is the same basal ring as in the Semantida and Coronida. The former is a "mitral ring," developed in the same manner, by union of two pairs of horizontal lateral branches, which arise on both sides from the apical rod (or mitral rod) of the sagittal ring. In the simplest case these two parallel horizontal rings are connected only by the sagittal ring, which is either complete (Protympanium, Pl. 93, fig. 14) or incomplete (Parastephanus, Pl. 93, fig. 21). But commonly also an incomplete frontal ring is present, so that the two horizontal rings are connected by four vertical or subvertical rods; two of these "columellæ" are the dorsal and ventral rods of the sagittal ring, the two others are the lateral rods of the frontal ring. Between the former and the latter are sometimes developed two, four, or more accessory columellæ (probably halves of accessory incomplete diagonal meridian rings). In this way arise the characteristic "drum-forms" of many Tympanida, in which the two parallel horizontal rings correspond to the upper and lower rings of a drum, whilst the connecting vertical columellæ correspond to its parallel lateral rods (Pl. 83, figs. 1, 2, &c.).

Originally the two horizontal rings of these "drum-shells" are both bisected by the complete sagittal ring, each provided with two lateral gates (Protympanida). But in the Eutympanida both rings exhibit one simple gate only, the apical and the basal rod of the sagittal ring being lost. In the Paratympanida both rings are closed by a secondary lattice-plate whilst in the Dystympanida the upper (mitral) ring alone is closed by such a plate, the lower (basal) ring is open. In some Eutympanida the shell assumes the strange form of a regular geometrical cube, the twelve edges of which are represented by thin rods of silex (Lithocubus)—its four upper edges represent the mitral ring, the four lower the basal ring; two opposite of the four vertical cube-edges are the lateral halves of the frontal ring, the two other alternate ones are the remaining halves of the reduced sagittal ring (dorsal and ventral rod) (Pl. 82, fig. 12).

In many Tympanida and Coronida a loose irregular lattice or framework is developed, which partly closes the large open gates. But this never reaches the completeness of a true lattice-shell, such as we find in the Spyroidea, Botryodea, and Cyrtoidea. In by far the greater number of Stephoidea the corners, and partly also the rods, of the shell are armed with numerous irregular spines, often forked or richly branched. Among these spines the descending "basal apophyses" possess a peculiar importance, since by their regular number and disposition they correspond to the radial rods of the Plectoidea, and to the typical "feet" of the Spyroidea and Cyrtoidea. The most important of them are the three cortinar feet (one caudal and two pectoral) of Cortina, Cortiniscus, &c. (compare above, p. 891).

The Central Capsule exhibits in the Stephoidea the same characteristic structure as in all other Monopylea, first exactly pointed out by Richard Hertwig in 1879 (Organismus der Radiol., p. 71, Taf. vii. figs. 4, 5). Its form is commonly ovate or ellipsoidal, sometimes also lentelliptical or nearly spherical. It exhibits constantly on the basal pole the porochora or porous area, and in the basal half the podoconus or pseudopodial cone. From the surrounding sagittal ring it is separated by a thick jelly-like calymma, which commonly exhibits numerous zooxanthellæ. The numerous pseudopodia are commonly branched, with rather rare anastomoses. The membrane of the central capsule is thick.

Synopsis of the Families of Stephoidea.

I. Skeleton composed of the simple vertical sagittal ring only, without secondary rings, 1. Stephanida.

II. Skeleton composed of two crossed rings, a vertical sagittal and a horizontal basal ring, 2. Semantida.

III. Skeleton composed of two crossed vertical meridional rings (a primary sagittal and a secondary frontal ring), commonly also with a horizontal basal ring, 3. Coronida.

IV. Skeleton composed of two parallel horizontal rings (upper mitral and lower basal ring), both connected by a vertical sagittal ring (and often by a vertical frontal ring), 4. Tympanida.

Family XLVIII. Stephanida, Haeckel (Pl. 81).

Definition.—Stephoidea with a simple sagittal ring, without any lattice-work.

The family Stephanida is the most simple of all Stephoidea, and probably the common ancestral group of this suborder (compare above, p. 933). The skeleton consists of a simple ring only, surrounding the central capsule, and armed commonly with simple thorns or with larger branched spines. The branches of these spines are constantly free, never joining together. Therefore the shell exhibits no trace of fenestration or lattice-work, no pores or gates, except the simple large gate of the ring itself. In all other Stephoidea we find secondary gates or lattice-work.

The first known form of this family is Lithocircus annularis, described by Johannes Müller in 1858 (Abhandl. d. k. Akad. d. Wiss. Berlin, p. 29, Taf. i. fig. 1). He observed already the central capsule ("Blase") surrounded by the circular ring of silex, and the calymma ("Strahlige Gallert") enveloping the whole body. The peculiar structure of the soft body, particularly the "area porosa" on the basal pole of the central capsule, and the pseudopodial cone within it, were first accurately described by Hertwig (in 1879). A great number of simple rings, similar to these, were found in the Challenger collection, and are here arranged in six genera and forty-eight species.

The simple ring of silex, which alone forms the skeleton of the Stephanida, corresponds to the primary or sagittal ring of the other Stephoidea, and lies therefore vertically in the median or sagittal plane of the body. We can therefore distinguish on it four different segments, rods or bows, two of which are more horizontal, two more vertical. The former are one upper bow or apical rod, and one lower bow or basal rod. The latter are one posterior bow or dorsal rod, and one anterior bow or ventral rod. Sometimes each of these four component bows is distinguished by a corner-spine, or by a pair of divergent branches.

In the two simplest (and probably oldest) genera of Stephanida, in Archicircus and Lithocircus, the dorsal and ventral rods of the ring are equal and cannot be distinguished; therefore the fundamental form is here amphithect, diphragmatic, or biradial (the poles of the sagittal axis being equal). In the four other genera the dorsal rod is more straight (often vertical) and more or less different from the ventral, convexly curved rod; therefore the fundamental form is here dipleuric or bilateral, as in the greater number of all Nassellaria (the poles of the sagittal axis being unequal). The general form of the ring in this latter case is commonly obliquely ovate or nearly triangular, the basal pole being more pointed, the apical pole more rounded (Pl. 81).

The rods or bows of the ring are either roundish or cylindrical (with circular or elliptical transverse section), or they are prismatic or angular (commonly with triangular transverse section). In the latter case one edge usually is prominent in the sagittal plane (on the convex outside of the ring), whilst two other edges diverge laterally on both sides of it. The inner or concave margin of the ring is commonly smooth.

The inner perimeter of the large gate, enclosed by the ring, is commonly rounded (elliptical or ovate), rarely angular. However, the outer perimeter of the ring is nearly always polygonal, with prominent corners, and usually from these arise thorns or branched spines which are regularly disposed. Regarding this disposition we may distinguish three cases: A, the spines lie in the sagittal plane and form a single row, arising from the median edge; B, the spines lie on both sides of the latter and form two parallel rows, arising from the two lateral edges; C, the spines represent a combination of A and B, and are disposed in three rows, two paired rows arising from the two lateral edges, and an odd middle row between them, arising from the median edge. The spines are simple, without branches, in Archicircus and Zygocircus; more or less branched in Lithocircus and Dendrocircus. The branches are often richly ramified or arborescent, and exhibit great variety in size, special form, and direction (compare Pl. 81).

The number and disposition of the spines or groups of spines are usually constant, and may be employed in the further progress of our knowledge, to distinguish a number of genera and subgenera. Very commonly (perhaps in the majority of the Stephanida) we find six groups of spines, an apical group on the upper rod of the sagittal ring, a basal group on the lower rod (on the porochora of the central capsule), two ventral groups on the anterior rod, and two dorsal groups on the posterior rod. In other species we find four or eight groups instead of six, and sometimes a larger number.

The most important of these apophyses of the ring are the basal spines, arising from its basal pole, where the porochora of the central capsule rests upon it. They are often much larger and more branched than the other spines, and attain a peculiar morphological value in the small subfamily Cortinida. Here we find three or four regularly disposed "basal spines," which may be compared to the typical "basal feet" of the Cyrtellaria, appearing in the majority of Spyroidea and Cyrtoidea. Cortina, one of the most important Nassellaria, bears three typical divergent feet on the base of the simple ring, two paired anterior or "pectoral feet," and an odd posterior or "caudal foot." The latter appears as a direct basal prolongation of the dorsal rod of the ring, and is opposed to an upper prolongation of the same, which corresponds to the "apical horn" of the Cyrtellaria (Pl. 97, figs. 1-3). As already explained above, these three basal feet of Cortina possess the highest phylogenetic value, since they may also be compared with the three primary radial spines of the Plectoidea, and so connect the Cyrtellaria and the Plectellaria. Stephanium differs from Cortina in the possession of four basal feet, an odd anterior or "sternal foot" being added to the three typical feet of the latter (Pl. 92, figs. 20, 21). Some forms of Plectoidea (Plagoniscus, Plectaniscus, &c.) seem to be nearly related to these Cortinida, and may be easily transformed into them by development of a complete ring, embracing the central capsule. They seem to demonstrate the near affinity of all these triradiate Nassellaria (Pl. 91, figs. 4, 5, 9, 10).

Synopsis of the Genera of Stephanida.

I. Subfamily Lithocircida. No typical basal feet on the base of the ring (no cortinar feet). Ring diphragmatic or amphithect; dorsal and ventral bow equal. Ring smooth or thorny, without branched spines. 401. Archicircus.

Ring armed with branched spines, 402. Lithocircus.

Ring dipleuric, bilateral; dorsal and ventral bow different. Ring smooth or thorny, without branched spines, 403. Zygocircus.

Ring armed with branched spines. 404. Dendrocircus.

II. Subfamily Cortinida. Three or four typical basal feet on the ring (cortinar feet). Three basal feet (and an apical horn). One caudal and two lateral feet, 405. Cortina.

Four basal feet (and an apical horn). Two sagittal and two lateral feet, 406. Stephanium.

I. Subfamily Lithocircida. No typical basal feet on the base of the ring (no cortinar feet).

Ring diphragmatic or amphithect; dorsal and ventral bow equal.

Ring smooth or thorny, without branched spines.

401. Archicircus.

Ring armed with branched spines,

402. Lithocircus.

Ring dipleuric, bilateral; dorsal and ventral bow different.

Ring smooth or thorny, without branched spines,

403. Zygocircus.

Ring armed with branched spines.

404. Dendrocircus.

II. Subfamily Cortinida. Three or four typical basal feet on the ring (cortinar feet).

Three basal feet (and an apical horn).

One caudal and two lateral feet,

405. Cortina.

Four basal feet (and an apical horn).

Two sagittal and two lateral feet,

406. Stephanium.

Subfamily 1. Lithocircida, Haeckel.

Definition.—Stephanida without typical basal feet or cortinar feet.

Genus 401. Archicircus,^[20] n. gen.

Definition.—Stephanida with a simple amphithect or diphragmatic ring, smooth or thorny, without branched spines and basal feet.

The genus Archicircus is the most primitive and simplest form of all Stephoidea, and probably the common ancestral form, not only of this suborder, but of the greater number of all Nassellaria (compare above, p. 893). The skeleton consists only of a quite simple sagittal ring, in which commonly a slight difference of both poles of the main axis (basal and apical pole) is visible, but no difference between the dorsal and the ventral bow of the ring. In my Prodromus (1881, p. 447) the species of Archicircus were disposed partly in the subgenus Monostephus, partly in the genus Lithocircus.

Subgenus 1. Monostephus, Haeckel, 1881, Prodromus, p. 447.

Definition.—Ring circular, elliptical, or ovate, without prominent corners.

1. Archicircus princeps, n. sp.

Gate circular. Ring circular, smooth, its transverse section also circular. The simplest form of all Stephoidea.

Dimensions.—Diameter of the gate 0.05 to 0.08; thickness of the ring 0.006 to 0.008.

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

2. Archicircus monostephus, n. sp. (Pl. 83, fig. 17).

Gate circular. Ring circular, with three elegantly denticulate edges (one outer median and two lateral edges). Transverse section of the ring triangular.

Dimensions.—Diameter of the gate 0.06 to 0.08; thickness of the ring 0.01 to 0.008.

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

3. Archicircus ellipsis, n. sp.

Gate elliptical. Ring elliptical, on the inner margin smooth, on the outer margin with fifteen to twenty equal, short, simple, or slightly forked thorns. Transverse section ovate.

Dimensions.—Diameter of the gate 0.05 to 0.09; thickness of the ring 0.01 to 0.014.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms; also fossil in Barbados.

4. Archicircus ovalis, n. sp.

Gate ovate. Ring elliptical, smooth, with three prominent, slightly distorted edges, without thorns; in the transverse section triangular.

Dimensions.—Diameter of the gate 0.08 to 0.12; thickness of the ring 0.006 to 0.009.

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

5. Archicircus monopylus, n. sp.

Gate ovate. Ring ovate, thorny, with three distorted edges, in the transverse section triangular; surface covered with numerous simple small thorns arising from the three edges.

Dimensions.—Diameter of the gate 0.1 to 0.15; thickness of the ring 0.01 to 0.012.

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

Subgenus 2. Archistephus, Haeckel.

Definition.—Ring polygonal, with four to six or more prominent corners (and commonly with simple spines arising from the corners).

6. Archicircus quadratus, n. sp.

Gate square. Ring square, with three edges and four short simple pyramidal spines on the four corners, opposite in pairs in two perpendicular diameters. Transverse section triangular.

Dimensions.—Diameter of the gate 0.08; thickness of the ring 0.008.

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

7. Archicircus rhombus, n. sp. (Pl. 81, fig. 7).

Gate rhombic. Ring rhombic, with four prominent edges and four pairs of short, divergent, pyramidal spines on the four corners, arising from the lateral edges of the four rods, about as long as the radius of the gate.

Dimensions.—Diameter of the gate 0.04 to 0.08; thickness of the ring 0.007 to 0.01.

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

8. Archicircus duodenus, n. sp.

Gate square or rhombic. Ring rhombic, with three prominent edges and twelve stout and straight pyramidal spines, about as long as the radius of the gate. In each of the four corners are three divergent spines, arising from the three edges of each two meeting rods.

Dimensions.—Diameter of the gate 0.08; thickness of the ring 0.012.

Habitat.—North Atlantic, surface (Rabbe).

9. Archicircus primordialis, n. sp. (Pl. 81, fig. 1).

Gate ovate. Ring hexagonal, with three prominent edges and six short pyramidal thorns at the six corners; the basal thorn is either simple or forked.

Dimensions.—Diameter of the gate 0.07; thickness of the ring 0.01 to 0.015.

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

10. Archicircus hexacanthus, n. sp. (Pl. 81, fig. 4).

Gate subregular, hexagonal. Ring hexagonal, with three sharp edges and six equal radial pyramidal spines, arising from the six corners and placed in the plane of the ring, about as long as the diameter of the gate.

Dimensions.—Diameter of the gate 0.05 to 0.07; thickness of the ring 0.01.

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

11. Archicircus hertwigii, Haeckel.

Lithocircus annularis, R. Hertwig (non J. Müller), 1879, Organismus der Radiol., p. 69. Taf. vii. fig. 5.

Gate hexagonal, with prolonged main axis. Ring hexagonal, with two prominent edges and six pairs of equal, short, conical spines, arising from the two edges of the six rods at the six corners and divergent on each side of the plane of the ring. The basal spine-pair is doubled, therefore there are in all fourteen spines.

Dimensions.—Diameter of the gate 0.05 to 0.07; thickness of the ring 0.005 to 0.006.

Habitat.—Mediterranean (Messina), Hertwig, surface.

12. Archicircus triglyphus, n. sp.

Gate ovate. Ring hexagonal, with three prominent edges and twenty-two to twenty-four simple curved spines, arising from the six corners and about as long as the diameter of the gate. In the basal corner arise six to nine larger spines, protecting the basal pole of the central capsule. From each of the five other corners arise three spines, diverging from the three edges.

Dimensions.—Diameter of the gate 0.07 to 0.11; thickness of the ring 0.008 to 0.011.

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

13. Archicircus sexangularis, n. sp. (Pl. 81, fig. 12).

Gate hexagonal or subcircular. Ring hexagonal, with two sharp prominent edges and six pairs of divergent spines, about as long as the radius of the gate, and arising from the two edges at the six corners. The two apical and the two basal spines are simple and conical, whilst the eight other spines, arising in pairs from the two dorsal and the two ventral corners, are slightly forked.

Dimensions.—Diameter of the gate 0.06 to 0.08; thickness of the ring 0.01 to 0.015.

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

Genus 402. Lithocircus,^[21] J. Müller, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 484.

Definition.—Stephanida with a simple amphithect or diphragmatic ring, armed with branched spines, without typical basal feet.

The genus Lithocircus is the oldest known form of all Stephoidea, founded by J. Müller in 1856 for his Lithocircus annularis, the first species of this suborder described. We retain here this cosmopolitan form as the typical representative of the genus, which differs from the preceding Archicircus, its ancestral form, in the development of branched radial spines.

1. Lithocircus annularis, J. Müller.

Lithocircus annularis, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 29, Taf. i. fig. 1.

Gate circular. Ring circular, with four forked or simply branched spines, opposite in pairs in two diameters, perpendicular one to the other. Spines with slender curved fork-branches, about as long as the diameter of the gate. The specimen figured by J. Müller bears a supernumerary fifth spine; numerous other specimens observed by me exhibited a regular cross of four spines.

Dimensions.—Diameter of the gate 0.1 to 0.15; length of the spines 0.01 to 0.18.

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

2. Lithocircus quadricornis, n. sp. (Pl. 81, fig. 9).

Gate square. Ring square, with three sharp denticulate edges, and four large bunches of richly branched spines on the four corners. In each corner arise three curved spines, about as long as the diameter of the ring; their numerous irregular branches are forked and curved like the antlers of deer.

Dimensions.—Diameter of the gate 0.07; length of the horns 0.06 to 0.09.

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

3. Lithocircus decimalis, n. sp. (Pl. 81, fig. 15).

Gate elliptical. Ring pentagonal, with three prominent edges and five pairs of branched spines on the five corners. In each corner arise two or three curved spines, about as long as the radius of the gate, each with two to four forked branches.

Dimensions.—Diameter of the gate 0.08; length of the spines 0.03 to 0.05.

Habitat.—North Atlantic, Station 354, surface.

4. Lithocircus hexablastus, n. sp. (Pl. 81, fig. 17).

Gate elliptical. Ring hexagonal, with three prominent edges and six pairs of branched spines, arising from the six corners. Each of the twelve spines is short and stout, only half as long as the radius of the gate, and bears a bunch of ten to twenty short, densely aggregated, conical or horn-like curved branches.

Dimensions.—Diameter of the gate 0.1; length of the spines 0.02 to 0.03.

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

5. Lithocircus crambessa, n. sp. (Pl. 81, fig. 6).

Gate elliptical or subcircular. Ring hexagonal, with three wing-shaped distorted edges and six groups of branched spines, arising from the six corners. In each corner arise three short and stout divergent spines, each bearing a bunch of numerous short roundish branches like a cauliflower, scarcely as long as the thickness of the ring.

Dimensions.—Diameter of the ring 0.1 to 0.12, length of the spines 0.01 to 0.02.

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

6. Lithocircus tarandus, n. sp. (Pl. 92, fig. 19).

Gate circular. Ring hexagonal, with three sharp edges and six pairs of large branched spines, arising from the flat lateral edges on the six corners. Each of the twelve spines is horizontally expanded, longer than the diameter of the ring and dichotomously forked like the antlers of a reindeer. If the lateral ends of the branches of this species become united in the frontal plane, we get Microcubus, the four upper spines forming the mitral ring, the four middle the equatorial ring, and the four lower the basal ring.

Dimensions.—Diameter of the gate 0.08; length of the spines 0.09.

Habitat.—Central Pacific, Station 272, surface.

7. Lithocircus furcatus, n. sp.

Gate ovate. Ring ovate, with three sharp prominent edges. The two lateral edges are smooth. The median edge (in the sagittal plane) bears sixteen to twenty forked spines (commonly eight dorsal, eight ventral, and four basal). All the spines are of nearly equal size, slightly curved, and about half as long as the short sagittal axis of the ring.

Dimensions.—Diameter of the gate 0.08 to 0.12; length of the spines 0.03 to 0.04.

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

8. Lithocircus magnificus, n. sp. (Pl. 81, fig. 16).

Gate ovate or nearly elliptical. Ring ovate, with three prominent edges, and numerous richly branched spines arising from the three edges. The specimen figured, which I observed living in the Mediterranean, exhibited eight bunches of larger spines, three dorsal, three ventral, one apical, and one basal bunch; the latter much larger than the seven others. Each bunch was composed of two to four larger and numerous smaller spines, their branches curved and forked. The ovate purple central capsule, with a distinct podoconus, filled more than the half of the gate.

Dimensions.—Diameter of the gate 0.1 to 0.13; length of the spines 0.05 to 0.15.

Habitat.—Mediterranean (Portofino, 1880), Atlantic (Canary Islands), Station 354, surface.

Genus 403. Zygocircus,^[22] Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 496.

Definition.—Stephanida with a simple dipleuric or bilateral ring, smooth or thorny, without branched spines and basal feet.

The genus Zygocircus and the following Dendrocircus differ from the two preceding older genera in the bilaterally symmetrical or dipleuric form of the sagittal ring. Whilst in Archicircus and Lithocircus the two sagittal halves or bows of the ring, the dorsal and ventral bow, are equal (therefore the fundamental form amphithect or diphragmatic), here both bows become distinctly different; the dorsal bow is constantly more straight (often vertical), the ventral bow more convex (obliquely ascending). This dipleuric differentiation is most important, as it is transmitted to the greater number of Nassellaria by heredity.

1. Zygocircus sagittalis, n. sp.

Gate ovate. Ring half ovate or nearly triangular, with three curved edges and three prominent corners, one apical and two basal protuberances. Dorsal rod vertical, twice as long as the horizontal basal rod. Ventral rod convexly curved.

Dimensions.—Diameter of the gate 0.05 to 0.07; height of the tubercles 0.01 to 0.015.

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

2. Zygocircus trigonus, n. sp.

Gate triangular. Ring triangular, with three curved edges and three prominent corners, which are prolonged into nine divergent conical spines; three spines arising from the three edges of each corner. Dorsal rod vertical; ventral and basal rods curved and convergent.

Dimensions.—Diameter of the gate 0.11 to 0.13; length of the spines 0.01 to 0.015.

Habitat.—Indian Ocean, Sunda Archipelago (Rabbe), surface.

3. Zygocircus tetragonus, n. sp.

Gate ovate. Ring quadrangular, without edges, with four simple conical spines of different sizes; one smaller apical, one larger basal, and two equatorial spines of middle size (one dorsal and one ventral). Dorsal and ventral rod curved.

Dimensions.—Diameter of the gate 0.04 to 0.06; length of the spines 0.018 to 0.026.

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

4. Zygocircus rhombicus, n. sp.

Gate rhombic. Ring rhombic, with three prominent edges, and eight short conical curved spines arising from the lateral edges at the four corners of the rhombus. The basal and ventral spine are larger than the apical and dorsal spine; the ventral rod is more curved (with smaller angle) than the shorter dorsal rod. The medial edge of the ring is smooth, without spines.

Dimensions.—Diameter of the gate 0.08; length of spines 0.02 to 0.04.

Habitat.—South Atlantic, Station 335, depth 1425 fathoms.

5. Zygocircus pentagonus, n. sp. (Pl. 81, fig. 8).

Gate roundish pentagonal. Ring very thick (about as thick as the radius of the gate), irregularly pentagonal, with prominent sagittal edge. On both sides of the latter arise at the five corners five pairs of short simple irregularly curved spines. The four ventral spines are larger than the four dorsal, and the two basal spines larger than the eight former, forked. (In fig. 8 the basal spines are turned upwards.)

Dimensions.—Diameter of the gate 0.07; length of the spines 0.04 to 0.06.

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

6. Zygocircus hexagonus, n. sp.

Gate irregularly hexagonal. Ring obliquely hexagonal, thick, without edges, with six short and stout conical spines on the six corners. The two spines of the curved ventral rod are longer than the two spines of the straight dorsal rod. The apical spine is smaller and the basal spine larger than the four others.

Dimensions.—Diameter of the gate 0.07 to 0.09; length of the spines 0.01 to 0.03.

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

7. Zygocircus triquetrus, n. sp. (Pl. 81, fig. 3).

Gate obliquely ovate. Ring obliquely hexagonal, with three sharp edges and three short conical spines on each of the six corners. Therefore each hexagonal edge bears six short radial spines of equal size.

Dimensions.—Diameter of the gate 0.04 to 0.08; length of the spines 0.01 to 0.02.

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

8. Zygocircus dodecanthus, n. sp.

Gate semicircular. Ring semicircular or irregularly hexagonal, without edges, with twelve short blunt spines, arising in pairs from the six corners; two apical, two basal, and between them two equatorial corners. Three pairs of spines remain on the straight dorsal rod, three on the curved ventral rod.

Dimensions.—Diameter of the gate 0.04 to 0.06; length of the spines 0.01 to 0.02.

Habitat.—Central Pacific, Stations 263 to 268; depth 2650 to 2900 fathoms.

9. Zygocircus acacia, n. sp. (Pl. 81, fig. 5).

Gate obliquely ovate. Ring semi-ovate, with straight dorsal and curved ventral rod, partly with distorted edges. Six bunches of numerous short and straight conical spines arise from the ring, one larger bunch (often trifid) from the apex, two smaller bunches from the dorsal, two from the ventral rod, and one very large bunch from the base. The six bunches are often more separated, smaller, and the spines shorter than in the figured specimen, which passes over into Dendrocircus.

Dimensions.—Diameter of the gate 0.12 to 0.16; length of the spines, 0.01 to 0.07.

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

10. Zygocircus polygonus, n. sp. (Pl. 81, fig. 2).

Gate irregularly roundish or ovate. Ring irregularly polygonal or sometimes nearly circular, without edges, armed with a single series of ten to fifteen short pyramidal spines, which are irregularly disposed in the sagittal plane. The ventral rod is strongly curved, often semicircular, the dorsal rod less curved or nearly straight.

Dimensions.—Diameter of the gate 0.05 to 0.07; length of the spines 0.004 to 0.02.

Habitat.—Cosmopolitan—Atlantic, Pacific; also fossil in Barbados.

11. Zygocircus bütschlii, n. sp.

Zygocircus productus, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 497.

Gate obliquely ovate. Ring irregularly roundish, semi-ovate or ovate, with interrupted and distorted edges, and with a large number (ten to twenty or more) of simple, irregularly formed and asymmetrically disposed spines; commonly some larger spines at the base.

Dimensions.—Diameter of the gate 0.05 to 0.09; length of the spines 0.005 to 0.02.

Habitat.—Fossil in Barbados.

12. Zygocircus productus, Bütschli.

Zygocircus productus, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi p. 496.

Lithocircus productus, R. Hertwig, 1879, Organismus d. Radiol., p. 69, Taf. vii. fig. 4.

Gate obliquely ovate. Ring obliquely ovate, with three complete prominent edges and with numerous (ten to twenty or more) simple, short conical spines, arising in three series from the three edges; commonly some smaller spines at the base.

Dimensions.—Diameter of the gate 0.1 to 0.2; length of the spines 0.005 to 0.02.

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

Genus 404. Dendrocircus,^[23] Haeckel, 1881, Prodromus, p. 447.

Definition.—Stephanida with a simple dipleuric or bilateral ring, armed with branched spines, without typical basal feet.

The genus Dendrocircus has the same dipleuric or bilaterally symmetrical form of the sagittal ring as its ancestral genus Zygocircus. It differs from the latter in the development of branched radial spines, and therefore bears to it the same relation as the amphithect Lithocircus does to the simpler Archicircus.

1. Dendrocircus quadrangulus, n. sp.

Gate irregularly quadrangular or nearly semicircular. Ring quadrangular, edgeless, with four unequal sides; ventral rod more curved and with longer sides than the dorsal rod. From the four edges arise four strong, irregularly branched spines, about as long as the diameter of the gate, with curved branches; the ventral and basal spines larger than the dorsal and apical spines. Similar to Lithocircus quadricornis (Pl. 81, fig. 9), but less branched, and with a striking difference between the shorter dorsal and the longer ventral rod.

Dimensions.—Diameter of the gate 0.04 to 0.06; length of the spines 0.05 to 0.07.

Habitat.—North Pacific, Station 256, depth 2950 fathoms.

2. Dendrocircus dodecarrhiza, n. sp.

Gate obliquely ovate. Ring irregularly quadrangular, with three prominent edges. From the latter arise at the four corners twelve divergent, irregularly branched spines (three in each corner), about as long as the radius of the gate, with curved branches; the three basal spines larger than the nine others.

Dimensions.—Diameter of the gate 0.08 to 0.1; length of the spines 0.04 to 0.06.

Habitat.—Indian Ocean (Maldive Islands), surface (Haeckel).

3. Dendrocircus dodecancistra, n. sp. (Pl. 81, fig. 11).

Gate obliquely ovate or nearly elliptical. Ring irregularly ovate, with three distorted edges and six pairs of branched spines. The two ventral pairs are much more distant than the two dorsal pairs, the ventral rod being longer and more curved than the dorsal rod. All twelve spines are of nearly equal size, are more or less curved, about as long as the diameter of the gate, and each bears six to twelve irregular short branches at the end.

Dimensions.—Diameter of the gate 0.07 to 0.08; length of the spines 0.05 to 0.08.

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

4. Dendrocircus arborescens, n. sp. (Pl. 81, fig. 10).

Gate irregularly roundish or nearly circular. Ring of the same form, with slight edges and six pairs of elegant arborescent spines (one apical, two dorsal, two ventral, and one basal pair); the three latter somewhat larger than the three former. Each tree is larger than the ring, in the basal half simple, in the distal half forked, each fork-branch with numerous dichotomous terminal branches.

Dimensions.—Diameter of the gate 0.06 to 0.08; length of the spines 0.12 to 0.15.

Habitat.—Central Pacific, Stations 266 to 274, surface.

5. Dendrocircus elegans, n. sp. (Pl. 81, fig. 13).

Gate irregularly ovate. Ring thick, ovate, with three denticulate edges and six bunches of stout, branched and spinulate, curved spines. The four ventral spines are more distant than the four dorsal, the ventral rod being more curved than the dorsal. The latter bears above the two apical spines. The two basal spines are much larger, deeply forked; their four fork-branches may be compared to the four basal feet of Stephanium.

Dimensions.—Diameter of the ring 0.09 to 0.11; length of the spines 0.03 to 0.06.

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

6. Dendrocircus barbadensis, n. sp.

Gate irregularly ovate or nearly semicircular. Ring of the same oblique form, thick, with interrupted and distorted edges, armed with eight to twelve larger irregularly formed and branched acute spines; between them numerous conical smaller spines. This common species is very polymorphous and variable.

Dimensions.—Diameter of the ring 0.05 to 0.08; length of the spines 0.005 to 0.02.

Habitat.—Fossil in Barbados.

7. Dendrocircus stalactites, n. sp. (Pl. 81, fig. 14).

Gate obliquely ovate. Ring irregularly ovate or roundish, very thick, without edges, armed with numerous (eight to twelve or more) short and stout branches, which are shorter than the diameter of the gate, irregularly disposed and branched, with very numerous clustered blunt ramules.

Dimensions.—Diameter of the gate 0.07 to 0.09; length of the spines 0.02 to 0.06.

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

Subfamily 2. Cortinida, Haeckel.

Definition.—Stephanida with typical basal feet (or cortinar feet).

Genus 405. Cortina,^[24] n. gen.

Definition.—Stephanida with a simple dipleuric or bilateral ring, bearing at the base three divergent feet (one odd caudal and two paired lateral feet).

The genus Cortina and the following Stephanium represent together the small but very important group of Cortinida, differing from the simple Lithocircida in the possession of three typical basal feet, which are transmitted to the majority of the Nassellaria by heredity, and produce their peculiar triradial structure. They appear therefore as a combination of the simple ring (Zygocircus) with three basal feet (Plagonium). One of these three divergent feet is the odd caudal foot, opposite to the apical horn; the two others are the paired lateral or pectoral feet. (On the probable origin and the typical signification of Cortina compare above, pp. 891-894.)

1. Cortina tripus, n. sp. (Pl. 83, fig. 9).

Ring ovate, smooth, or with a few short thorns. Apical horn oblique, curved, simple, smooth, about as long as the sagittal axis of the ring. Feet divergent, curved, simple, smooth, about as long as the horn; the caudal foot shorter than the two pectoral feet. Very variable in form and size.

Dimensions.—Height of the ring 0.06 to 0.09, breadth 0.04 to 0.06; length of the feet 0.05 to 0.1.

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

2. Cortina typus, n. sp. (Pl. 97, fig. 1).

Ring kidney-shaped or nearly semicircular, with revolute vertical dorsal rod and strongly curved ventral rod; both rods with two pairs of spine-bunches. Apical horn nearly straight, thorny, longer than the ring, directed a little obliquely backwards. Feet slightly curved, of equal length, two to three times as long as the ring; each armed with few large bunches of curved spines, which are more developed in the caudal foot than in the two pectoral feet.

Dimensions.—Height of the ring 0.14, breadth 0.08; length of the feet 0.2 to 0.3.

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

3. Cortina conifera, n. sp.

Ring subcircular, smooth. Apical horn and the three divergent feet of equal size and similar form, cylindrical, straight, about as long as the ring, at the distal end thickened, with a dimply cone (similar to Tripospyris conifera and Tripospyris eucolpa, Pl. 84, figs. 4, 7).

Dimensions.—Height of the ring 0.08, breadth 0.06; length of the feet 0.09.

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

4. Cortina furcata, n. sp.

Ring elliptical, with three forked horizontal spines (one on the dorsal and two on the ventral rod). Apical horn and the three divergent feet of equal size, somewhat longer than the ring, slightly curved, in the distal half forked.

Dimensions.—Height of the ring 0.07, breadth 0.05; length of the feet 0.09.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms. Fossil in Barbados.

5. Cortina dendroides, n. sp.

Ring ovate, with six pairs of branched horizontal spines, three on the dorsal and three on the ventral rod. Apical horn very large, arborescent, about as long and as broad as the ring. Feet similar to the horn, also richly branched, of equal size. All the rods and their branches curved, with prominent distorted edges.

Dimensions.—Height of the ring 0.13 to 0.17, breadth 0.1 to 0.12; length of the feet 0.15 to 0.2.

Habitat.—Central Pacific, Stations 266 to 274, depth 2350 to 2925 fathoms.

6. Cortina cervina, n. sp. (Pl. 92, fig. 21).

Ring ovate, with four pairs of forked horizontal spines (two dorsal and two ventral pairs). Apical horn straight and stout, as long as the ring, with trifid point. Three feet equal, widely divergent, very large, branched like a deer's antler, with very numerous short and stout, curved and pointed branches. All rods and branches roundish, without edges.

Dimensions.—Height of the ring 0.1, breadth 0.07; length of the feet 0.12 to 0.16.

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

Genus 406. Stephanium,^[25] n. gen.

Definition.—Stephanida with a simple dipleuric or bilateral ring, bearing at the base four divergent feet (two sagittal and two lateral feet).

The genus Stephanium differs from the preceding nearly allied Cortina in the production of four basal feet; the new foot, missing in the latter, is the anterior or sternal foot. Therefore Stephanium may be regarded as the archetype of all those Nassellaria in which, on the base of the sagittal ring, there are developed four typical feet—two sagittal feet (the posterior caudal and anterior sternal foot) and two lateral feet (right and left). On the origin of Stephanium compare above, p. 893, &c.

1. Stephanium quadrupes, n. sp. (Pl. 92, fig. 20).

Ring ovate, with three prominent dentate edges and a short pyramidal apical horn. Four feet all of nearly equal size, about as long as the ring, also with three thorny edges, in the upper half divergent, in the lower convergent.

Dimensions.—Height of the ring 0.12, breadth 0.08; length of the feet 0.11 to 0.13.

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

2. Stephanium tetrapus, n. sp.

Ring elliptical, without edges, thorny, with a stout, thorny apical horn of the same length. Four feet curved and irregularly branched, divergent, of different size. The two sagittal feet (the anterior sternal and posterior caudal) about as long as the ring. The two lateral feet (right and left) nearly twice as long, more richly branched.

Dimensions.—Height of the ring 0.16, breadth 0.11; length of the feet 0.15 to 0.3.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms. Fossil in Barbados.

Family XLIX. Semantida, n. fam.

Definition.—Stephoidea with a single vertical ring (the primary sagittal ring), bearing on its base a horizontal ring (basal or cortinar ring) with two to four or more basal gates (or cortinar pores).

The family Semantida differs from the preceding Stephanida in the development of a small horizontal ring on the base of the primary vertical sagittal ring. By the crossing of these two rings a small latticed basal plate is formed, with one or two pairs of pores; rarely with a greater number of "basal pores." The production of this characteristic "basal plate" is of the greatest morphological importance, as the beginning of the numerous different lattice-formations, which are differentiated in the great majority of Nassellaria.

In my Prodromus (1881, p. 446) I had enumerated the Semantida with three genera (Nos. 298 to 300) as a separate subfamily of the Dyostephida or "Stephoidea biannularia," and characterised these "Dyostephanida" by the following definition: "Skeleto annulis duobus composito, qui in duobus planis invicem perpendicularibus jacent; altero annulo (sagittali) verticali, altero (basali) horizontali." As the names there given were already employed with another signification, and as the Zygostephanida (there united with the Dyostephanida) are more closely related to the Coronida, I now change the names, and propose to call the family Semantida, expressing by this term the typical similarity of the skeleton to a signet-ring (Semantis, Semantrum, Semantidium).

At about the same time, some Stephoidea of this family were accurately described by Bütschli (1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 495, Taf. xxxii. figs. 6, 7, 8). He called them Stephanolithis, a name which Ehrenberg had employed, not for complete shells of Radiolaria, but for isolated parts of such, and for siliceous fragments of different skeletons, needles of Sponges, &c. The three species described by Bütschli represent three different genera of our Semantida, viz., Semantis spinescens (with two gates in the basal plate), Semantrum mülleri (with four gates), and Semantidium haeckelii (with six gates). He pointed out the great morphological value of the fenestrated basal plate and its paired gates, as beginnings of numerous other Nassellaria. But his opinion, that in all Spyroidea and Cyrtoidea, derived from these, two pairs of basal gates were constant, was erroneous, nor was the formation of the first pair naturally explained; he supposed that the formation of the basal plate begins by development of an odd sagittal apophysis, arising from the base of the primary sagittal ring. But this odd sagittal apophysis ("der unpaare mediane Kieselfortsatz c1", loc. cit., p. 497) is in reality not a primary and essential part of the skeleton, but secondary and of little morphological value, absent in the majority of the Semantida and of the other Nassellaria.

We divide our family Semantida into two different subfamilies, which possibly possess a direct phylogenetic relation to the two subfamilies of Stephanida:—The Semantiscida have no typical feet, and have arisen directly from the Lithocircida; the Cortiniscida, however, possess the three typical basal feet of Cortina, and may therefore be derived directly from the Cortinida. Since these three cortinar feet are probably identical with the three primary radial rods of the Plectoidea, an immediate affinity also to these Nassellaria is indicated.

The Semantiscida, which do not possess these three basal cortinar feet, are the simpler forms of the family. The simplest of all, and perhaps the common ancestral form of the whole family, is Semantis (Pl. 92, figs. 1, 2). It may be derived from Archicircus or Zygocircus by development of two pairs of horizontal apophyses on its base, around the porochora of the central capsule. The two rods of each side (right and left), becoming curved one towards the other, and meeting laterally, form a simple horizontal gate, and the two paired basal gates together, a horizontal ring or basal ring, to which the primary sagittal ring is perpendicular. In the next allied genus, Semantrum (Pl. 92, figs. 3-5), three pairs of horizontal apophyses are developed, and therefore two pairs of basal gates produced, an anterior and a posterior. In the third genus, Semantidium (Pl. 92, figs. 6, 7), three pairs of basal pores or gates are visible, surrounded and separated by four pairs of horizontal apophyses, which arise from the base of the sagittal ring. Finally, in Clathrocircus (Pl. 92, figs. 8-10) the number of apophyses is much increased, and two parallel rows of pores are developed along the two sides of the sagittal ring.

The basal plate or the "seal," developed from the base of the primary sagittal ring or "signet-ring," is therefore a horizontal ring, which becomes bisected by the latter, and exhibits either one pair of primary "basal gates" or two or three pairs of these important basal pores, rarely more. Since these pores possess the greatest morphological value, and are probably everywhere homologous, we give to them and to the separating apophyses certain names, and call the anterior pair of gates, "jugular pores" (i in our figures, the pair I of Bütschli); the middle (usually the largest) pair, "cardinal pores" (k in our figures, the pair II of Bütschli), and the posterior, smaller pair, "cervical pores," l. The typical pairs of rods, by the union of which these basal pores arise, are the following:—(1) the clavicular or furcular rods, f, the first pair (rods e1 of Bütschli), (2) the coracal rods, e, between the jugular and cardinal pores (rods e of Bütschli), (3) the scapular rods, g, between the cardinal and cervical pores (rods e2 of Bütschli), (4) the cervical rods, the fourth pair of apophyses, the most posterior, h. Bütschli supposes that the topographical succession of the three typical pairs of basal pores is also the chronological succession, the jugular being formed first, the cardinal second and the cervical pores third but it seems that this succession is often altered and that the cardinal pores (the largest), appear first, the jugular pores (in front of them) second and the cervical pores third (or perhaps sometimes in the inverse succession).

The Cortiniscida, the second subfamily of Semantida, differ from the preceding Semantiscida in the possession of three typical basal feet, which are probably inherited from the Cortinida, and perhaps indirectly from the Plagonida (Plagoniscus). The simplest and the most important form of this second family is Cortiniscus (Pl. 92, figs. 11-13), differing from its probable ancestral form, Cortina, in the development of a basal ring, produced by horizontal union of the basal apophyses. The three typical feet are the same as in all triradiate Nassellaria, two paired pectoral feet (p₁, p₁₁) diverging on the anterior base of the sagittal ring, whilst the odd caudal foot (c) lies on its posterior base in the sagittal plane and appears as a basal prolongation of the dorsal rod of the sagittal ring; the upper part of the dorsal rod is usually prolonged into an ascending apical horn. In Stephaniscus (Pl. 92, figs. 14, 15) four basal feet are visible, an anterior or sternal foot (z) being added as a prolongation of the basal rod of the ring, opposite to the caudal foot. Finally, Semantiscus (Pl. 92, figs. 16-18) is distinguished by the possession of six divergent basal feet, probably identical with those of all six-radiate Nassellaria; three of these may be regarded as primary and perradial, the odd caudal and the paired pectoral feet; the three other intercalated as secondary or interradial feet, the odd sternal (z) and the paired tergal feet (t₁, t₁₁).

The basal plate of these Cortiniscida exhibits the same important differences as in the preceding Semantiscida, either one, or two, or three pairs of basal gates being developed. But there occur also in some species (mainly in Cortiniscus) only three basal gates, an odd anterior (between the two pectoral feet and a connecting horizontal bar), and two paired posterior (between the two pectoral and the odd caudal foot). It requires further accurate researches to solve the important problem, what the true homologies of these typical basal pores and the separating bars are in the different genera of Semantida. In Semantiscus there are three pairs of basal pores in the horizontal seal, corresponding to those of Semantidium and the radial rods or bars between, these are the basal parts of the six radial feet; therefore the odd caudal foot (t) seems to be the posterior, and the odd sternal foot (z) the anterior prolongation of the basal part of the primary sagittal ring; the two paired anterior or pectoral feet (p₁, p₁₁) the prolongations of the coracal rods (e) and the two paired posterior or tergal feet (t₁, t₁₁), the prolongations of the scapular rods (g). But it is not yet certain whether these six radial feet and the separating gates of the basal plate are all the same and truly homologous in all six-radiate Nassellaria. In every case the comparative study of the Semantida is of the highest value for the accurate knowledge of the Monopylea.

Synopsis of the Genera of Semantida.

I. Subfamily Semantiscida. Basal ring without typical, regularly disposed basal feet (no cortinar feet). Only two, four, or six basal pores (no dorsal and ventral pores). Two basal pores, 407. Semantis.

Four basal pores, 408. Semantrum.

Six basal pores, 409. Semantidium.

Besides four basal pores, also apical pores or dorsal and ventral pores along the whole ring, 410. Clathrocircus.

II. Subfamily Cortiniscida. Basal ring with typical, regularly disposed basal feet (cortinar feet). Three basal feet. One odd caudal foot and two paired lateral feet, 411. Cortiniscus.

Four basal feet. Two sagittal and two lateral or pectoral feet, 412. Stephaniscus.

Six basal feet. Two sagittal, two pectoral, and two tergal feet, 413. Semantiscus.

I. Subfamily Semantiscida. Basal ring without typical, regularly disposed basal feet (no cortinar feet).

Only two, four, or six basal pores (no dorsal and ventral pores).

Two basal pores,

407. Semantis.

Four basal pores,

408. Semantrum.

Six basal pores,

409. Semantidium.

Besides four basal pores, also apical pores or dorsal and ventral pores along the whole ring,

410. Clathrocircus.

II. Subfamily Cortiniscida. Basal ring with typical, regularly disposed basal feet (cortinar feet).

Three basal feet.

One odd caudal foot and two paired lateral feet,

411. Cortiniscus.

Four basal feet.

Two sagittal and two lateral or pectoral feet,

412. Stephaniscus.

Six basal feet.

Two sagittal, two pectoral, and two tergal feet,

413. Semantiscus.

Subfamily 1. Semantiscida, Haeckel.

Definition.—Semantida without typical basal feet or cortinar feet.

Genus 407. Semantis,^[26] n. gen.

Definition.—Semantida with two basal pores (or jugular pores), without typical basal feet.

The genus Semantis, the most primitive and the oldest of the Semantida, is of the greatest morphological interest, as the first form of Stephoidea which produces gates or pores by communicating branches, and therefore the probable ancestral form not only of this family, but of the greater number of all Stephoidea, and perhaps even of all Spyroidea and Cyrtoidea. Semantis arises from Archicircus by the production of two pairs of lateral branches from the basilar rod of the sagittal ring, one anterior pair of clavicular rods, and one posterior pair of coracal rods. By junction of the clavicular and coracal rod on each side arises a left and a right pore, the "jugular pore or jugular gate."

1. Semantis biforis, n. sp. (Pl. 92, fig. 2).

Sagittal ring obliquely ovate, nearly trapezoidal, with six pairs of short mammillated knobs or branches; dorsal rod straight, vertical, with two pairs of knobs, ventral rod strongly convex, also with two pairs of knobs; two other pairs in the apical rod. Basilar rod horizontal, straight. Basal ring with six pairs of similar knobs, three on each side. Basal gates ovate or nearly triangular.

Dimensions.—Height of the sagittal ring 0.09, breadth 0.07.

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

2. Semantis distoma, n. sp.

Sagittal and basal ring nearly of the same form as in the preceding species, but half as thick and armed with numerous branched spines which are about half as long as the diameter of the main gate, and with thin and curved pointed branches.

Dimensions.—Height of the sagittal ring 0.11, breadth 0.08.

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

3. Semantis dipyla, n. sp.

Sagittal ring kidney-shaped, very thick, with six pairs of short, thorny, or irregularly tuberculated knobs (two dorsal, two apical, and two ventral pairs). Basal ring smooth, scarcely half as thick, horizontal, with two semicircular basal gates, about half as broad as the main gate. From the two opposite lateral corners of the basal ring two slender upwardly curved spines arise, resembling the basal part of a commencing frontal ring.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.05.

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

4. Semantis sigillum, n. sp. (Pl. 92, fig. 1).

Sagittal ring elliptical, with four pairs of stout arborescent spines (two apical and two equatorial pairs), which are irregularly branched and forked, with numerous thin lateral branches. Apex with a short conical trifid vertical horn. Basal ring thorny, with obliquely descending slightly curved bars.

Dimensions.—Height of the sagittal ring 0.12, breadth 0.09.

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

5. Semantis distephanus, n. sp. (Pl. 83, fig. 3).

Sagittal ring thin, semicircular, smaller than the thin basal ring, which exhibits two semicircular gates. Both rings are armed with numerous small spines of equal size, which on the former are arranged in two, on the latter in three regular rows. (The basal rod of the sagittal ring, separating the two basal gates, in fig. 3 is, by mistake, not distinctly enough drawn.)

Dimensions.—Height of the sagittal ring 0.06, breadth 0.08.

Habitat.—Tropical Atlantic, Station 348, surface.

6. Semantis spinescens, Haeckel.

Stephanolithis spinescens, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p.160, Taf. i. fig. 29.

Stephanolithis spinescens, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 497, Taf. xxxii. figs. 7a, 7b.

Sagittal ring ovate with four pairs of thin, irregularly branched spines, two apical pairs, one on the straight dorsal rod and one on the curved ventral rod. Basilar rod with a posterior and an anterior forked rod (commencing caudal and sternal foot). Basal ring square, with two lateral spines, and two triangular gates scarcely one-third as broad as the ring-gate. An internal ascending procolumna (rod c₁ in the figure of Bütschli) connects the basal and ventral rods of the sagittal ring.

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

Habitat.—Fossil in Barbados.

Genus 408. Semantrum,^[27] n. gen.

Definition.—Semantida with four basal pores (two anterior jugular and two posterior cardinal pores), without typical basal feet.

The genus Semantrum, one of the most important of the Nassellaria, arises from the preceding Semantis by duplication of the two basal gates. Behind the pair of coracal rods there arises from the basilar rod of the sagittal ring a third pair of lateral horizontal branches, the scapular rods. These become connected with the coracal rods on each side, and so produce a second posterior pair of basal pores, the "cardinal gates." These are constantly larger than the anterior "jugular gates." Therefore the vertical ring of Semantrum possesses a horizontal basal ring with four very characteristic gates, enclosed by three pairs of lateral curved and connected branches, and these become transmitted by heredity to the majority of the Nassellaria.

1. Semantrum quadrifore, n. sp. (Pl. 92, fig. 5).

Sagittal ring subcircular or ovate, with three edges and four sagittal forked spines on the odd edge (two dorsal and two ventral spines). Basal ring decagonal, with ten simple or forked spines on the ten corners. Jugular gates tetragonal. Cardinal gates pentagonal.

Dimensions.—Height of the sagittal ring 0.09, breadth 0.07.

Habitat.—Tropical Atlantic, Station 351, surface.

2. Semantrum tetrastoma, n. sp. (Pl. 92, fig. 3).

Sagittal ring semicircular, thorny, without edges. Basal ring tetragonal or nearly cordate, with a small anterior and a large posterior bow-shaped incision; on the lateral edges with numerous irregular thorns. Jugular gates pear-shaped. Cardinal gates nearly kidney-shaped.

Dimensions.—Height of the sagittal ring 0.1 to 0.14, breadth 0.07 to 0.09.

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

3. Semantrum tetrapylum, n. sp.

Sagittal ring elliptical, tuberculate. Basal ring trapezoidal, also with roundish thick rods and small irregular tubercles on the margin. Jugular gates ovate, two-thirds as broad as the triangular cardinal gates.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.05.

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

4. Semantrum mülleri, Haeckel.

Stephanolithis mülleri, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi pp. 499, 539, Taf. xxxii. figs. 8a, 8b, 8c.

Sagittal ring nearly semicircular or obliquely ovate, thorny. Basal ring also nearly semicircular, with two slight sagittal incisions (one anterior and one posterior), on the lateral edges with numerous small thorns. Jugular pores (pair I of Bütschli) pear-shaped. Cardinal pores (pair II of Bütschli) triangular. Sometimes (but not constantly) a pair of cervical bows connects the scapular bars with the subvertical dorsal rod of the sagittal ring.

Dimensions.—Height of the sagittal ring 0.09, breadth 0.06.

Habitat.—Fossil in Barbados.

5. Semantrum sphragisma, n. sp.

Sagittal ring circular, smooth. Basal ring also nearly circular and smooth; its four basal gates of nearly equal size, elliptical or subcircular; the jugular pores scarcely smaller than the cardinal pores. All rods smooth, cylindrical, without edges and thorns.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.07.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms; also fossil in Barbados.

6. Semantrum bütschlii, n. sp.

Sagittal ring triangular, with vertical straight ascending dorsal rod, horizontal straight basilar rod and obliquely ascending, slightly curved ventral rod; all rods nearly cylindrical, with irregular branched thorns and distorted edges. Jugular pores triangular, scarcely half as broad as the large semicircular cardinal pores.

Dimensions.—Height of the sagittal ring 0.11, breadth 0.08.

Habitat.—Fossil in Barbados.

7. Semantrum signarium, n. sp. (Pl. 92, fig. 4).

Sagittal ring obliquely ovate, thorny. Basal ring kidney-shaped or nearly pentagonal, with broad concave dorsal incision and five larger branched spines on the five corners; between them smaller thorns. Jugular gates pear-shaped, scarcely half as broad as the triangular cardinal gates.

Dimensions.—Height of the sagittal ring 0.12, breadth 0.09.

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

Genus 409. Semantidium,^[28] n. gen.

Definition.—Semantida with six basal pores (two anterior jugular, two middle cardinal, and two posterior cervical pores), without typical basal feet.

The genus Semantidium exhibits a further developmental stage of the basal plate of the Semantida. Whilst this plate in Semantis possesses one pair of basal pores, and in Semantrum two pairs, here in Semantidium it has three pairs. The new third pair is produced on the dorsal edge of the basal plate, which becomes connected with the basal part of the dorsal rod of the sagittal ring by a pair of cervical rods. The middle pair of pores (the cardinal) are always larger than the anterior (jugular) and the posterior (cervical pores). The same form of basal plate is preserved in numerous Spyroidea and Cyrtoidea, as a "cortinar septum with six collar pores," (e.g., Pl. 53, fig. 18).

1. Semantidium hexastoma, n. sp. (Pl. 92, fig. 6).

Sagittal ring ovate, thorny. Basal ring rhombic or nearly square, with four short conical descending spines on the four prominent edges (two sagittal and two lateral); between them numerous smaller irregular thorns. Jugular and cervical gates nearly equal, ovate, half as broad as the triangular cardinal gates between them.

Dimensions.—Height of the sagittal ring 0.14, breadth 0.1.

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

2. Semantidium sexangulum, n. sp.

Sagittal ring ovate, with six pairs of short branched thorns (two apical, two dorsal, and two ventral). Basal ring hexagonal, with three pairs of short branched thorns on the six corners (one sagittal pair, one posterior and one anterior). All six gates of the basal plate triangular, the jugular and cervical a little smaller than the cardinal gates.

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

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

3. Semantidium haeckelii, Bütschli.

Stephanolithis Haeckelii, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. pp. 499, 538, Taf. xxxii. figs. 6a, 6b.

Sagittal ring elliptical, with three pairs of short horizontal branched spines, one apical and two equatorial pairs (one dorsal and one ventral). Basal ring roundish hexagonal, with numerous short thorns on the margin. Jugular pores ovate, about half as broad as the ovate cardinal pores and twice as broad as the small cervical pores.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.06.

Habitat.—Fossil in Barbados.

4. Semantidium signatorium, n. sp. (Pl. 92, fig. 7).

Sagittal ring semicircular, thorny; basal ring pentagonal, with short spines on the margin and five stronger thorny spines on the five corners. Jugular pores ovate, smaller than the triangular cervical pores. Cardinal pores two to three times as large as each of the former, pentagonal.

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

Habitat.—North Pacific, Station 341, depth 2300 fathoms.

Genus 410. Clathrocircus,^[29] Haeckel, 1881, Prodromus, p. 447.

Definition.—Semantida with a variable number of pores on the apical and the basal part of the ring, symmetrically arranged, without typical basal feet.

The genus Clathrocircus comprises those Semantida in which the sagittal ring bears not only basal pores (as in the three preceding genera) but also apical pores (on the opposite pole of the main axis), or a variable number of pores along the whole ring. All these pores are symmetrically arranged in pairs. In the simplest form there are only two apical pores opposite to four basal pores, whilst in the highest state of development the whole ring bears two complete circles of pores. At both poles of the transverse axis two large lateral gates remain open. If these become closed by lattice-work, Clathrocircus passes over into Dictyospyris.

1. Clathrocircus hexaporus, n. sp.

Sagittal ring circular, smooth, with three pairs of pores (one apical and two basal). The two apical pores are triangular with two lateral spines, and correspond to the two mitral gates of the Tympanida. The four basal pores form a hexagonal basal plate, with six lateral spines, and correspond to the four basal pores of Semantrum; the two jugular are pear-shaped, and half as broad as the two triangular cardinal pores.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.06.

Habitat.—Cosmopolitan; Atlantic, Pacific, many Stations, surface.

2. Clathrocircus octoporus, n. sp.

Sagittal ring elliptical, smooth, with four pairs of pores (two apical and two basal). The four apical pores are of nearly equal size, subcircular, and form a regular cross around the apical pole. The four basal pores are ovate, and form a quadrangular plate, armed with marginal thorns; the two jugular pores are somewhat smaller than the two cardinal pores.

Dimensions.—Height of the sagittal ring 0.11, breadth 0.08.

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

3. Clathrocircus decaporus, n. sp.

Sagittal ring ovate, thorny, with five pairs of pores (two apical and three basal). The four apical pores are roundish and form a cross. The six basal pores are triangular and form a hexagonal plate with thorny margin; the two jugular pores are somewhat larger than the two cervical, and half as broad as the two cardinal pores.

Dimensions.—Height of the sagittal ring 0.09, breadth 0.07.

Habitat.—North Pacific, Station 256, depth 2950 fathoms.

4. Clathrocircus stapedius, n. sp. (Pl. 92, fig. 8).

Sagittal ring ovate, smooth, with six pairs of pores (two apical and four basal). The four apical pores are of nearly equal size and form a quadrangular mitral plate with two large lateral horns. The eight basal pores are of very different size (the four central far larger than the two anterior and the two posterior), and form a hexagonal basal plate, also with two large lateral horns. The four branched lateral horns (two upper and two lower) form together an incomplete frontal ring.

Dimensions.—Height of the sagittal ring 0.1, breadth 0.08.

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

5. Clathrocircus dictyospyris, n. sp. (Pl. 92, fig. 9).

Sagittal ring ovate, thorny, with eight pairs of pores. The four apical and the four basal pores are elliptical and far larger than the four dorsal and the four ventral pores. Resembles a Dictyospyris with open lateral gates.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.06.

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

6. Clathrocircus multiforis, n. sp. (Pl. 92, fig. 10).

Sagittal ring circular, smooth, with ten to twelve pairs of roundish pores, forming together a complete lattice-girdle with two parallel circular rows of pores. Four larger of these are the four gates of the basal ring (two jugular and two cardinal pores).

Dimensions.—Diameter of the ring 0.1 to 0.15, breadth 0.03 to 0.05.

Habitat.—Central Pacific, Stations 263 to 274, depth 2350 to 2925 fathoms.

Subfamily 2. Cortiniscida, Haeckel.

Definition.—Semantida with large, typical, regularly disposed basal feet (originally three cortinar feet, one odd caudal and two paired pectoral).

Genus 411. Cortiniscus,^[30] n. gen.

Definition.—Semantida with three typical basal feet (an odd caudal foot and two paired lateral or pectoral feet).

The genus Cortiniscus is of peculiar importance, as the common ancestral form of the Cortiniscida, or those Semantida in which the basal ring is provided with typical, regularly disposed basal feet—three, four, or six. Since these typical basal feet (or "cortinar feet") are preserved in the greater number of all Nassellaria, determining their triradial structure, they possess a great morphological value. Cortiniscus exhibits the same three primary feet as Cortina, from which it differs in the production of two or more basal pores (between the odd caudal and the paired lateral feet).

1. Cortiniscus tripodiscus, n. sp. (Pl. 92, fig. 11).

Sagittal ring ovate, thorny, with three prominent, distorted edges; its dorsal rod nearly straight and vertical, with one or two pairs of short thorns; its ventral rod strongly curved, with three or four pairs of divergent thorns. Basal ring larger than the sagittal ring, with two semicircular gates and obliquely ascending halves, which on the inner and lower edge are smooth, on the outer and upper thorny. Apical horn and the three divergent feet nearly equal, straight, about as long as the sagittal ring, with three thorny edges.

Dimensions.—Height of the sagittal ring 0.1 to 0.12, breadth 0.07 to 0.09.

Habitat.—Central Pacific, Stations 270 to 274, depth 2350 to 2925 fathoms.

2. Cortiniscus dipylaris, n. sp. (Pl. 92, fig. 13).

Sagittal ring nearly semicircular, with prominent distorted edges and six pairs of small roundish papillate tubercles (three pairs on the straight dorsal, three on the curved ventral rod). Apical horn short and stout, with a tuberculate knob. Basal ring smaller than the sagittal ring with two elliptical gates. Three feet short and stout, irregularly branched like a cauliflower, with numerous short papillate tubercles.

Dimensions.—Height of the sagittal ring 0.11, breadth 0.08.

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

3. Cortiniscus tripylaris, n. sp.

Sagittal ring elliptical, smooth. Apical horn conical, smooth. Basal ring larger than the sagittal ring, with three elliptical gates of equal size; two paired, posterior (jugular pores) between the basal parts of the caudal foot and the two pectoral feet, and an odd, anterior (sternal pore) between the basal parts of the two pectoral feet and a connecting horizontal convex sternal bow.

Dimensions.—Height of the sagittal ring 0.09, breadth 0.06.

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

4. Cortiniscus tetrapylaris, n. sp.

Sagittal ring elliptical, with four pairs of short branched thorns, two posterior on the straight dorsal, and two anterior on the curved ventral rod. Basal ring smaller than the sagittal ring, with four triangular gates; the two anterior (jugular pores) a little smaller than the two posterior (cardinal pores). Apical horn and the three divergent feet shorter than the sagittal ring, irregularly branched, with curved, often tuberculate branches.

Dimensions.—Height of the sagittal ring 0.08 to 0.12, breadth 0.06 to 0.1.

Habitat.—Fossil in Barbados.

5. Cortiniscus typicus, n. sp. (Pl. 92, fig. 12).

Sagittal ring ovate, thorny, with three distorted edges; dorsal rod nearly straight and vertical prolonged upwards into a stout thorny apical horn, downwards into the caudal foot. Basal ring smaller than the sagittal ring, with four elliptical or nearly triangular gates; the two anterior (jugular pores) about half as large as the two posterior (cardinal pores). Three feet of equal size, thorny, divergent, straight or slightly curved, about as long as the diameter of the sagittal ring.

Dimensions.—Height of the sagittal ring 0.14 to 0.18, breadth 0.1 to 0.12.

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

Genus 412. Stephaniscus,^[31] n. gen.

Definition.—Semantida with four typical basal feet (two sagittal and two lateral or pectoral feet).

The genus Stephaniscus differs from the preceding Cortiniscus in the production of a fourth (sternal) foot, and therefore exhibits the same relation to it that Stephanium among the Stephanida bears to Cortina. It differs from Stephanium, in the production of a basal ring, with pores or gates between the bases of the basal feet. Two of these feet are sagittal (the posterior caudal and the anterior sternal foot), whilst the other two are lateral or pectoral (right and left). The basal lattice-plate exhibits either two pores ("jugular gates") or four pores (two anterior jugular and two posterior cardinal gates).

1. Stephaniscus tetrapodius, n. sp.

Sagittal ring nearly circular, smooth, with a short conical apical horn. Basal ring square, smooth, with two triangular gates. Four feet simple, equal, conical, divergent, about as long as the diameter of the ring.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.07.

Habitat.—Central Pacific, Stations 270 to 274, depth 2350 to 2925 fathoms.

2. Stephaniscus quadrifurcus, n. sp. (Pl. 92, fig. 14).

Sagittal ring subcircular, thorny with a small thorny apical horn. Basal ring also nearly circular, with two large semicircular gates and a few small thorns. All four feet curved and forked, the fork-branches again ramified, with numerous short curved and pointed branches. The two lateral feet (right and left) are larger and more branched than the two sagittal feet (sternal and caudal foot).

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

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

3. Stephaniscus quadrigatus, n. sp. (Pl. 92, fig. 15).

Sagittal ring oblique, ovate, with three prominent thorny edges; its dorsal rod nearly straight and vertical, the ventral rod strongly curved; apex with a small curved horn. Basal ring with a few short thorns and four gates of different size; the two anterior (jugular pores) ovate or nearly triangular, two-thirds as broad as the two posterior subcircular or pentagonal (cardinal pores). All four feet simple, curved, with three edges, the posterior (caudal) foot larger, the anterior (sternal) foot smaller than the two lateral (pectoral) feet.

Dimensions.—Height of the sagittal ring 0.09, breadth 0.07.

Habitat.—Tropical Atlantic, Station 351, surface.

4. Stephaniscus medusinus, n. sp.

Sagittal ring elliptical, thorny, with a larger apical horn. Basal ring nearly square, with short marginal thorns and four large ovate gates of nearly equal size. All four feet of equal size divergent, curved, irregularly branched, with short curved branches.

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

Habitat.—South Atlantic, Station 332, depth 2200 fathoms. Fossil in Barbados.

Genus 413. Semantiscus,^[32] n. gen.

Definition.—Semantida with six typical basal feet (two sagittal, two pectoral, and two tergal feet).

The genus Semantiscus may be the archetype of those Nassellaria which exhibit six typical basal feet, in combination with the sagittal ring. Three of these are the primary feet of Cortina and Cortiniscus, the other three are secondary productions between the former. The basal ring may possess either two, four, or six basal pores.

1. Semantiscus hexapodius, n. sp. (Pl. 92, fig. 16).

Sagittal ring elliptical, with a large branched apical horn. Basal ring small, square, with two small triangular gates (or jugular pores). From its periphery there arise six short and stout cylindrical feet, one very large (caudal) from the posterior corner, two tergal on each side, two opposite (pectoral) from the lateral corners, and one odd sternal from the anterior corner. All six spines bear a bunch of ten to twenty stout pointed conical branches, partly simple, partly forked.

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

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

2. Semantiscus hexaspyris, n. sp. (Pl. 92, fig. 18).

Sagittal ring semicircular, broad, latticed, with two pairs of irregular dorsal and two pairs of ventral pores. The dorsal rod is straight and vertical, prolonged upwards into a short serrate apical horn, downwards into a straight linear caudal foot. The ventral rod is curved and prolonged into a similar sternal foot. Basal ring hexagonal, with four ovate gates (two smaller jugular and two larger cardinal pores); its four lateral corners prolonged into four curved thorny lateral feet (two anterior larger pectoral, and two posterior smaller tergal feet). This species may be regarded as a commencing Hexaspyris or Liriospyris.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.06.

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

3. Semantiscus hexapylus, n. sp. (Pl. 92, fig. 17).

Sagittal ring ovate, thorny, with a small apical horn. Basal ring with six roundish or nearly triangular gates; the two jugular pores are smaller than the two cardinal and larger than the two cervical pores. The separating bars between these six pores are prolonged into six straight, thorny widely divergent feet; three larger feet (the caudal and the two pectoral) with a pair of apophyses, three smaller between them simple (the sternal and the two tergal feet).

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

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

Family L. Coronida, Haeckel.

Definition.—Stephoidea with two crossed vertical rings, perpendicular one to the other (the primary sagittal and the secondary frontal ring). Usually their common base bears a horizontal basal ring, but a mitral ring (or a horizontal ring at the apex) is never developed.

The family Coronida comprises those Stephoidea in which the primary sagittal ring (of the Stephanida and Semantida) becomes crossed by a second vertical ring, the lateral or frontal ring. Between these two vertical meridian rings, perpendicular to one another, four large apertures remain constantly open, the "lateral" gates. But besides these four constant openings, usually (excepting only in the Zygostephanida) other gates are developed on the common base of the two crossed rings, produced by a third, horizontal, basal ring. These basal gates are the same which we have found already in the Semantida.

The distinction of the Coronida from the other Stephoidea is always easy. In the Stephanida and Semantida, the frontal ring, or the second meridian ring, which we find in all Coronida, is never developed. On the other hand these latter never exhibit the typical "mitral ring," or the second, upper, horizontal ring, which distinguishes the Tympanida.

We distinguish here, among the Coronida, four different subfamilies, which perhaps afterwards may be better separated as families. Of these four groups the Zygostephanida and Acanthodesmida exhibit the nearest relationship to the Stephanida, whilst the Eucoronida and Trissocyclida possess a closer affinity with the Semantida.

The Zygostephanida, constituting the first subfamily, exhibit four large gates only, and differ from all other Coronida in the absence of a basal ring and of basal gates. Therefore the skeleton is entirely composed of two crossed vertical rings, perpendicular to one another; the first is the primary or sagittal ring (inherited from the Stephanida), the second is the new lateral or frontal ring. The four large lateral gates are either quite simple (Zygostephanus) or partly closed by loose and irregular lattice-work (Zygostephanium). The Zygostephanida may be derived directly from the Stephanida by development of lateral branches forming a frontal ring. They commonly possess the same characteristic spines or branches, and the same typical difference between the straight dorsal rod and convex ventral rod of the sagittal ring, which we found in the greater number of Stephanida. The frontal ring is commonly elliptical or kidney-shaped, and much larger than the ovate sagittal ring.

The Acanthodesmida, forming the second subfamily of Coronida, differ from all other members of this family in the possession of a large simple basal gate, surrounded by a simple horizontal basal ring. Only this ring is complete, whilst the two crossed vertical meridian rings (the primary sagittal and the secondary frontal ring) are incomplete, both truncated at the base by the basal ring. Therefore there remain here between the three rings five large gates (recognised previously by Johannes Müller in 1856 in Acanthodesmia): four lateral gates (the same as in the Zygostephanida) and one central basal gate. The latter is always quite simple and serves for the emission of the pseudopodia, arising from the basal pole of the central capsule. The four lateral gates are either quite simple (Coronidium) or partly closed by irregular loose lattice-work (Acanthodesmia). The subfamily Acanthodesmida may be derived either directly from the Stephanida (by development of a central basal gate) or from the Eucoronida (by loss of the basilar part of the sagittal ring).

The Eucoronida, the third subfamily, are the most important group of the Coronida; their numerous species are much more frequent and more widely distributed than those of the other three subfamilies. They may be derived immediately from the Semantida by the development of a lateral or frontal ring. This remains incomplete in the basal part, whilst the two other rings, perpendicular to it (the vertical sagittal ring and the horizontal basal ring), are complete. Therefore the shell constantly exhibits six large open gates between the three rings; four lateral gates (the same as in the Zygostephanida and Acanthodesmida) and two basal gates (inherited from Semantis); the latter correspond to the "jugular pores" of the Spyroidea and Cyrtoidea; they remain constantly simple. The four lateral gates may also remain simple (Eucoronis) or they may become partly closed by irregular loose lattice-work (Plectocoronis). The remarkable genus Podocoronis is distinguished by the development of typical descending basal feet, which are regularly disposed and correspond to the typical "cortinar feet" of the other Nassellaria. There may be developed either two lateral feet (as lower prolongations of the segments of the frontal ring), or three feet (one caudal and two pectoral, as in Cortina and Cortiniscus), or four feet (two sagittal and two lateral, as in Stephanium and Stephaniscus), or six feet (two sagittal, two pectoral, two tergal, as in Semantiscus), sometimes numerous feet (as in Petalospyris and Anthocyrtis, &c.).