Legion I. SPUMELLARIA, (continued 14)

Dimensions.—Radius of the principal posterior arm 0.2, of the anterior 0.15, of each lateral arm 0.1; greatest breadth (in the width) 0.01, basal breadth 0.03.

Habitat.—North Atlantic, Færöe Channel, Gulf Stream, surface, John Murray.

Genus 235. Histiastrum,^[274] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Definition.—Porodiscida with four simple, undivided, chambered arms, connected by a patagium; square shell a regular cross, with four equal arms and four right angles between them.

The genus Histiastrum, quite insufficiently characterised by Ehrenberg (1847), was afterwards (1875) illustrated by the figures of two different fossil species. One of these, Histiastrum ternarium, with three arms, belongs to Hymeniastrum; the other, Histiastrum quaternarium, is here retained as the true, typical representative species of the genus. It differs from its ancestral form Stauralastrum, by the possession of a patagium, from Tessarastrum by the regular square form of the shell.

Subgenus 1. Histiastrella, Haeckel.

Definition.—Distal ends of the arms blunt, without terminal spines.

1. Histiastrum quadrigatum, n. sp. (Pl. 46, fig. 3).

Arms at their distal end nearly as broad as long, and four times as broad as at their narrow base; their lateral edges concave, their terminal edge convex, without spines. Each arm is divided by seven to eight convex transverse septa into eight to nine simple, broad chambers. Central disk with three to four rings, about as broad as the fifth chamber. Patagium complete, connecting all the lateral edges of the arms.

Dimensions.—Radius of each arm 0.15, basal breadth 0.03, terminal breadth 0.12.

Habitat.—Equatorial Atlantic, Station 347, surface.

2. Histiastrum excisum, n. sp.

Arms four times as long as broad at their base, and twice as broad at their rounded blunt distal end as at their base; their lateral edges rectilinear, divergent. Central disk with three to four rings, somewhat broader than their distal end. Patagium incomplete, connecting only the basal half of the arms, with three to four concave chamber-rows, on the margin concave. (May be regarded as Euchitonia mülleri, with four arms.)

Dimensions.—Radius of each arm 0.2, basal breadth 0.05, distal breadth 0.1.

Habitat.—Atlantic, surface, Canary Islands.

3. Histiastrum velatum, n. sp. (Pl. 46, fig. 4).

Dictyastrum velatum, Haeckel, 1879, Atlas (pl. xlvi. fig. 4).

Arms pear-shaped, rapidly increasing from their narrow base, nearly circular, little longer than broad; each with eight to nine transverse chamber-rows; their lateral edges at their base concave, at their end circular. Central disk with three to four rings, somewhat smaller than one arm. Patagium complete, with six to seven radial beams, filling out perfectly the intervals between the arms. A peculiar girdle of finer network and equal breadth surrounds the whole equatorial periphery of the disk, and gives it the appearance of a square with rounded corners.

Dimensions.—Radius of each arm 0.2, basal breadth 0.03, distal breadth 0.12.

Habitat.—South Atlantic, Station 330, surface.

Subgenus 2. Histiastromma, Haeckel.

Definition.—Distal ends of the arms spiny, furnished with one or more terminal spines.

4. Histiastrum quaternarium, Ehrenberg.

Histiastrum quaternarium, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 74, Taf. xxiv. figs. 3, 4.

Arms six times as long as broad at their base, with rectilinear, little divergent edges; at their truncated distal end a little broader, with one single, very strong, conical, terminal spine. Central disk with four to five rings, somewhat broader than the arm. Patagium incomplete, enveloping only the basal half of the arms.

Dimensions.—Radius of each arm 0.18, basal breadth 0.03, distal breadth 0.05.

Habitat.—Fossil in the rocks of Barbados.

5. Histiastrum gladiatum, n. sp.

Astromma sp., Bury, 1862, Polycystins of Barbados, pl. v. fig. 1.

Arms triangular, eight times as long as broad at their base; at their distal end three times as broad as at their base, with rectilinear, divergent edges; their truncated end with a large conical, terminal spine. Central disk with four to five rings, broader than the arms. Patagium incomplete, enveloping only the basal half of the arms.

Dimensions.—Radius of each arm 0.12, basal breadth 0.013, distal breadth 0.04.

Habitat.—Fossil in the rocks of Barbados; and living in the depth of the Central Pacific, Station 268, depth 2900 fathoms.

6. Histiastrum boseanum, n. sp. (Pl. 46, fig. 1).

Arms linear, twelve times as long as broad at their base (at their distal end twice as broad as at their base), with rectilinear, parallel edges. The club-shaped end thickened, dentate, with two lateral rows of strong teeth in the equatorial plane, and with one very stout, angular, terminal spine. Central disk with two to three rings, broader than the arms. Patagium incomplete, with four to five concave chamber-rows, enveloping only the basal half of the arms. I call this splendid species in honour of Dr. Graf Bose, the great friend of nature and patron of the University of Jena.

Dimensions.—Radius of each arm 0.25, basal breadth 0.02, distal breadth 0.05.

Habitat.—Indian Ocean, Madagascar, Rabbe.

7. Histiastrum coronatum, n. sp.

Stephanastrum sp., Bury, 1862, Polycystins of Barbados, pl. iv. fig. 1.

Arms linear, eight times as long as broad, with rectilinear parallel edges; the thickened, nearly spherical, distal end three times as broad, with five strong conical spines, one middle (perradial) larger and two smaller on each side of it. Central disk with two to three rings, of the same breadth as the terminal knot of the arms. Patagium incomplete, square, enveloping the arms, with the exception of the knot.

Dimensions.—Radius of each arm 0.16, basal breadth 0.02, terminal breadth 0.06.

Habitat.—Fossil in the rocks of Barbados.

8. Histiastrum circulare, n. sp.

Stephanastrum sp., Bury, 1862, Polycystins of Barbados, pl. xxiii. fig. 1.

Arms linear in their inner half, egg-shaped and three times as broad in their outer half, with ten to twelve strong terminal spines, the middle (perradial) larger, in all three times as long as broad. Central disk with three to four rings, broader than their distal knobs. Patagium nearly complete, circular, enveloping the whole arms, with exception of the outermost end.

Dimensions.—Radius of each arm 0.22, basal breadth 0.02, terminal breadth 0.06.

Habitat.—Fossil in the rocks of Barbados; and living in the depths of the Central Pacific, Station 268, depth 2900 fathoms.

9. Histiastrum pentadiscus, n. sp. (Pl. 46, fig. 2).

Arms in their inner half linear, twice as long as broad, in their outer half circular, three times as broad, with the same structure as the central disk, exhibiting three concentric rings around one central chamber. Patagium complete, spongy, with radiating beams, enveloping the whole disk, with the exception of the outermost end of the arms, which is armed with twelve to sixteen strong conical spines, the middle (perradial) spine much larger.

Dimensions.—Radius of each arm (without terminal spine) 0.18, basal breadth 0.025, terminal breadth 0.08.

Habitat.—South Atlantic, Station 333, surface.

Genus 236. Tessarastrum,^[275] n. gen.

Definition.—Porodiscida with four simple, undivided, chambered arms, connected by a patagium; quadrangular shell bilateral, two opposite arms of the main axis (or principal arms) different from the two others (or lateral arms).

The genus Tessarastrum, formerly united by me with Histiastrum, differs from the latter in its bilateral or symmetrical form, and bears therefore the same relation to it that Hagiastrum does to Stauralastrum.

Subgenus 1. Tessarastrella, Haeckel.

Definition.—Both longitudinal arms of equal size and form.

1. Tessarastrum straussii, n. sp. (Pl. 45, fig. 8).

Histiastrum straussii, Haeckel, 1881, Prodromus et Atlas (pl. xlv. fig. 8).

Cross not rectangular. Both principal arms of equal size and form, four times as long as broad, and twice as long as the broader lateral arms; the former with ten to eleven, the latter with five to six joints, separated by convex transverse septa. Distal ends of the arms blunt. Axes of the smaller arms not perpendicular to that of the larger arms; therefore the anterior angles between them smaller than the posterior angles. Patagium between the arms incomplete. I call this remarkable species after the great German philosopher David Strauss.

Dimensions.—Radius of the principal arms 0.24, of the lateral arms 0.12; greatest breadth (in the middle) of the former 0.05, of the latter 0.06.

Habitat.—North Pacific, Hyalonema-ground, March 5, 1875.

2. Tessarastrum spinozæ, n. sp.

Cross rectangular. Both principal arms of equal size and form, ten times as long as broad, and twice as long as the lateral arms, which are only five times as long as broad. All arms linear, at their distal end club-shaped, and armed with twenty to thirty very strong angular spines. Patagium incomplete, enveloping only the basal half of the arms. (Resembles Histiastrum boseanum, Pl. 46, fig. 1, but differs in the broader arms and the unequal size of both pairs.) I call this species after the great monistic philosopher Benedictus Spinoza.

Dimensions.—Radius of the principal arms 0.3, of the lateral arms 0.16; basal breadth 0.025, distal breadth 0.05.

Habitat.—South Atlantic, Station 333, surface.

3. Tessarastrum brunonis, n. sp. (Pl. 45, fig. 9).

Histiastrum brunonis, Haeckel, 1881, Prodromus et Atlas (pl. xlv. fig. 9).

Cross rectangular. Both principal arms of equal size and form, three times as long as broad, each with ten joints, three times as long as the lateral arms, which are nearly square, with four joints. All arms rounded, at their truncated end little broader than at their base. No spines. Patagium complete, envelops the whole shell, and is composed of two parallel lattice-lamellæ on each side of the flat disk, which are connected by very fine perpendicular bars. This is shown clearly in fig. 9, Pl. 45, where the disk is seen from the edge. I call this species after the great Italian philosopher Giordano Bruno.

Dimensions.—Radius of the principal arms 0.22, of the lateral arms 0.12; basal breadth 0.04, distal breadth 0.05.

Habitat.—South Pacific, Station 285, depth 2375 fathoms.

Subgenus 2. Tessarastromma, Haeckel.

Definition.—The two principal arms of different size or form.

4. Tessarastrum democriti, n. sp. (Pl. 45, fig. 7).

Histiastrum democriti, Haeckel, 1881, Prodromus et Atlas (pl. xlv. fig. 7).

Cross not rectangular; the two anterior angles smaller than the two posterior. All four arms club-shaped, twice as broad at their rounded obtuse distal end as at their base, of unequal length. Posterior principal arm one and a fourth times as long as the posterior, and one and two-thirds as long as the lateral arms. Patagium incomplete, enveloping only the basal half of the arms. I call this species after the great Greek philosopher Democritus.

Dimensions.—Radius of the posterior arm 0.3, of the anterior 0.25, of each lateral arm 0.22; basal breadth 0.05, distal breadth 0.1.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

Genus 237. Stephanastrum,^[276] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Definition.—Porodiscida with four simple, undivided, chambered arms, connected on the distal ends by a spongy, square or rhomboidal, patagial girdle (or a patagium with four large, interbrachial openings). Shell either regular or bilateral (with equal or unequal arms).

The genus Stephanastrum, founded (1847) by Ehrenberg for the very peculiar Stephanastrum rhombus, differs from the nearly allied foregoing genera in the imperfect development of the peculiar patagium, connecting only the distal ends of the four arms, while it is absent at their base. Two new species, different from Stephanastrum rhombus by the regular square form, were found in the Challenger collection.

Subgenus 1. Stephanastrella, Haeckel.

Definition.—All four arms of the cross have the same size.

1. Stephanastrum quadratum, n. sp. (Pl. 46, fig. 5).

All four arms of the same size, six times as long as broad at their base, ending with a strong, short, four-sided pyramidal spine. In the outer half of each arm are two opposite lateral spongy wings, which form an equilateral triangle, and from union of the bases of the four triangles arises the peculiar patagium, which forms a square with four large interbrachial openings.

Dimensions.—Radius of each arm 0.25, basal breadth 0.035; length of the sides of the square patagium 0.3.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

2. Stephanastrum capitatum, n. sp. (Pl. 44, fig. 1).

All four arms of the same size, five times as long as broad at their base, at their distal end with a spongy, nearly spherical capitulum of twice their breadth, provided with a very strong, angular, pyramidal, terminal spine (half as long as the arm). All four arms connected by a square patagium, arising immediately below the capitula, and perforated by four large interbrachial openings.

Dimensions.—Radius of each arm (without the terminal spine) 0.25, basal breadth 0.05; length of the sides of the square patagium 0.3.

Habitat.—Pacific, central area. Station 265, depth 2900 fathoms.

Subgenus 2. Stephanastromma, Haeckel.

Definition.—Two opposite arms of the cross larger than the two others.

3. Stephanastrum rhombus, Ehrenberg.

Stephanastrum rhombus, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 33; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Taf. xxv. fig. 1.

Two arms of the longitudinal axis one and a third times as long as two arms of the transverse axis. All four arms linear, about eight times as long as broad, at their distal end somewhat thickened, club-shaped, with a pyramidal terminal spine. The ends of the arms are connected by a riband-shaped, straight, spongy patagium of the same breadth as the arms. Between the rhomboidal patagium and the arms remain four large rectangular triangles as interbrachial openings.

Dimensions.—Radius of the longer arms 0.2, of the shorter 0.15; basal breadth 0.02; length of the sides of the rhombic patagium 0.25.

Habitat.—Fossil in the rocks of Barbados.

Genus 238. Dicranastrum,^[277] Haeckel, 1881, Prodromus, p. 460.

Definition.—Porodiscida with four forked, spongy, or chambered arms, without a patagium; shell regular (not bilateral), with four equal arms crossed at right angles.

The genus Dicranastrum comprises a number of very remarkable, hitherto unknown, Euchitonida, which are rather common in the Pacific (mainly on the surface), and characterised by the bifurcation of the cross-arms of the regular square shell. It bears therefore to its probable ancestral form, Stauralastrum, the same relation that in the triradiate Euchitonida Chitonastrum does to Dictyastrum. The arms are commonly of very delicate structure, more or less spongy.

Subgenus 1. Dicranaster, Haeckel.

Definition.—Each cross-arm with two simple branches.

1. Dicranastrum furcatum, n. sp. (Pl. 47, fig. 2).

Arms simply forked, three times as long as broad at their base, with eight blunt ends of the fork-branches. The simple proximal half of each arm about the same size as each branch of the dichotomous distal part, twice as long as broad. Edges of the arms ragged.

Dimensions.—Radius of each arm 0.38, basal breadth 0.12; breadth of the forked part 0.3.

Habitat.—Pacific, central area, Station 271, surface.

2. Dicranastrum dichotomum, n. sp.

Arms simply forked, four times as long as broad at their base; each arm with two blunt branches. The simple proximal part of each arm is three times as long and twice as broad as each branch of the dichotomous distal part. Ends of the arms blunt, truncated.

Dimensions.—Radius of each arm 0.35, basal breadth 0.08; breadth of the forked part 0.2.

Habitat.—South Pacific, Station 281, surface.

3. Dicranastrum cornutum, n. sp. (Pl. 45, fig. 2).

Hagiastrum cornutum, Haeckel, 1879, Atlas (pl. xlv. fig. 2).

Four arms simply forked, four times as long as broad; each arm with two triangular diverging branches ending in strong conical spines. The simple basal part of each arm about of the same length as each branch of the distal part, twice as long as broad. Distance between the terminal spines of each arm nearly as great as its length.

Dimensions.—Radius of the arm 0.24, basal breadth 0.05; breadth across the bifurcation 0.12.

Habitat.—South Atlantic, Station 325, surface.

4. Dicranastrum antilope, n. sp.

Four arms simply forked, three times as long as broad; each arm with two lanceolate diverging branches, ending in strong angular spines. The simple basal part of each arm is twice as long as each branch of the distal part. Distance of the two terminal spines of each arm scarcely half as great as its length.

Dimensions.—Radius of the arm 0.32, basal breadth 0.11; breadth of the branches 0.07.

Habitat.—Tropical Atlantic (off Ascension), Station 342, surface.

Subgenus 2. Tricranastrum, Haeckel, 1881, Prodromus, p. 460.

Definition.—Each cross arm with three terminal branches, one middle (perradial) and two lateral (adradial) branches.

5. Dicranastrum wyvillei, n. sp. (Pl. 47, fig. 3).

Tricranastrum wyvillei, Haeckel, 1879, Natürl. Schöpfungsgesch., p. 705, Taf. xvi. fig. 5.

Arms trifid, one and a half times as long as broad; each arm with three blunt terminal branches of equal size. The simple basal part of each arm twice as long as the trifid distal part. (The central capsule depicted in fig. 3, Pl. 47, has the same form as the skeleton, and is only a little smaller.)

Dimensions.—Radius of the arm 0.4, basal breadth 0.12, greatest breadth (in the distal part) 0.24.

Habitat.—Pacific, central area, Station 271, surface.

6. Dicranastrum tricuspis, n. sp.

Arms trifid, twice as long as broad; each arm with three pointed terminal branches, ending in strong conical spines, the middle branch somewhat larger than the other two. The simple basal part of each arm three times as long as the trifid distal part.

Dimensions.—Radius of the arm 0.3, basal breadth 0.06, greatest breadth (in their distal part) 0.15.

Habitat.—North Pacific, Station 244, surface.

7. Dicranastrum trifarium, n. sp.

Arms trifid, three times as long as broad at their base; each arm with three pointed terminal branches, ending in strong sulcate spines; the middle branch twice as large as the two others. The simple basal part of each arm two and a half times as long as the trifid distal part.

Dimensions.—Radius of the arm 0.35, basal breadth 0.03, greatest breadth (in the distal part) 0.05.

Habitat.—South Pacific, Station 298, surface.

Subgenus 3. Tetracranastrum, Haeckel.

Definition.—Each cross-arm with four terminal branches, the two fork-branches being again bifurcated.

8. Dicranastrum bifurcatum, n. sp. (Pl. 47, figs. 1, 1a).

Arms doubly forked or quadripartite, six times as long as broad at their base; each arm in its proximal half simple, three times as long as broad; in its distal half doubly forked; the secondary branches with blunt, roundish ends, nearly as large as the primary branches. Central disk (fig. 1a) with three concentric rings around the central chamber; from its periphery radiate thin radial beams in the spongy framework of the delicate arms. The central capsule has the same form as the skeleton, and is only a little smaller.

Dimensions.—Radius of the arm 0.45, basal breadth 0.08; breadth of the terminal branches 0.03.

Habitat.—North Pacific, east of Japan, Station 241, surface.

Genus 239. Myelastrum,^[278] Haeckel, 1881, Prodromus, p. 460.

Definition.—Porodiscida with four forked, spongy, or chambered arms, without a patagium; shell bilateral, with paired different arms; two equal anterior arms of different shape from the two equal posterior arms.

The genus Myelastrum differs from the foregoing Dicranastrum, the ancestral form, by the twofold differentiation of the four arms. Whilst in the latter all four arms are equal, separated by equal angles, here the two anterior arms are constantly different from the two posterior. The lateral angles between the two arm-pairs are equal, while the posterior and the anterior angle (between the two arms of each pair) are more or less different. The shell assumes, therefore, a very characteristic bilateral form, similar to the "quadricorn cross" of the grey central substance in the transverse section of the human medulla spinalis. Though the spongy shell is commonly a most delicate and thin disk it nevertheless reaches unusual dimensions, its diameter in some species being more than a millimetre.

Subgenus 1. Myelastrella, Haeckel.

Definition.—Posterior arms simple, undivided; anterior arms lobated or cleft, with one or more incisions at the distal end.

1. Myelastrum medullare, n. sp. (Pl. 47, fig. 13).

Anterior arms bifid, nearly square, with a shallow incision at their broad truncated end. Posterior arms somewhat smaller, nearly triangular, with simple blunt ends. Sagittal constriction three-fourths as large as the transverse one. Surface smooth.

Dimensions.—Radius of the anterior arms 0.36, of the posterior 0.3; longitudinal constriction 0.24, transverse 0.36.

Habitat.—Pacific, central area, Station 271, surface.

2. Myelastrum spinale, n. sp.

Anterior arms bifid, twice as long as broad, with a deep incision at their truncated end. Posterior arms slender, half as large, with simple blunt ends. Sagittal constriction one and a half times as large as the transverse. Surface spiny.

Dimensions.—Radius of the anterior arms 0.4, of the posterior 0.2; longitudinal constriction 0.3, transverse 0.2.

Habitat.—North Pacific, Station 248, surface.

3. Myelastrum heteropterum, n. sp. (Pl. 47, fig. 8).

Anterior arms trifid, about as long as broad, with two incisions at their broad truncated end. Posterior arms about half as large, simple, with rounded blunt ends. Sagittal constriction two-thirds as large as the transverse. Surface bristly.

Dimensions.—Radius of the anterior arms 0.65, of the posterior 0.035; longitudinal constriction 0.4, transverse 0.6.

Habitat.—South Pacific, Station 291, surface.

Subgenus 2. Myelastromma, Haeckel.

Definition.—All four arms (posterior as well as anterior) lobated or cleft.

4. Myelastrum octocorne, n. sp. (Pl. 47, fig. 12).

All four arms with a deep incision in their distal half; anterior arms broader, but shorter than the posterior; in the anterior arms the two lobes are of the same size, in the posterior arms the median lobe is longer than the lateral lobe. Sagittal constriction little smaller than the transverse. Surface of the disk rough.

Dimensions.—Radius of the anterior arms 0.45, of the posterior 0.62; longitudinal constriction 0.25, transverse 0.3.

Habitat.—Pacific, central area, Station 271, surface.

5. Myelastrum farfalla, n. sp. (Pl. 47, fig. 10).

All four arms with a shallow incision at their distal end. Anterior arms broader, but shorter than the posterior; in each arm the anterior lobe is shorter than the posterior. Sagittal constriction smaller than the transverse. Surface smooth.

Dimensions.—Radius of the anterior arms 0.4, of the posterior 0.6; longitudinal constriction 0.5, transversal stricture 0.6.

Habitat.—Pacific, central area, Station 274, surface.

6. Myelastrum papilio, n. sp. (Pl. 47, fig. 6).

All four arms with a shallow incision at their distal end. Anterior arms triangular, of the same breadth, but of the double length of the square posterior arms. Sagittal and transverse constrictions of the same length. Surface ciliated. (Resembles a butterfly.)

Dimensions.—Radius of the anterior arms 0.7, of the posterior 0.4; longitudinal and transverse constrictions 0.4.

Habitat.—North Pacific, near Japan, Station 241, surface.

7. Myelastrum decaceros, n. sp. (Pl. 47, fig. 7).

Anterior arms bifid, with one shallow incision at their distal end. Posterior arms of the same length, but much broader, trifid, with two incisions (one larger and one smaller). Sagittal and transverse constrictions of the same length. Surface spiny.

Dimensions.—Radius of all four arms 0.4; longitudinal and transverse constrictions 0.35.

Habitat.—Pacific, central area, Station 272, surface.

8. Myelastrum dodecaceros, n. sp. (Pl. 47, figs. 11, 11a).

Anterior arms trifid, with two shallow incisions at their distal end. Posterior arms about one-third larger, also trifid, with one deeper anterior and one shallower posterior incision. Sagittal constriction much longer than the transverse. Surface ciliated, covered with numerous thin and long radial bristles (fig. 11a).

Dimensions.—Radius of the anterior arms 0.5, of the posterior 0.7; longitudinal constriction 0.5, transverse 0.35.

Habitat.—Pacific, central area, Station 270, surface.

9. Myelastrum ciliatum, n. sp.

Anterior arms trifid, with two shallow incisions. Posterior arms somewhat smaller, also trifid, with two deeper incisions. Sagittal constriction a little larger than the transverse. Margin of the disk ciliated, with radial bristle-shaped spines, as prolongations of the inner radial beams, arising from the central disk.

Dimensions.—Radius of the anterior arms 0.6, of the posterior 0.5; longitudinal constriction 0.4, transverse 0.35.

Habitat.—South Pacific, Station 288, surface.

10. Myelastrum lobatum, n. sp.

Anterior arms somewhat broader but shorter than the posterior arms. Each arm four-lobed, with three terminal shallow incisions of nearly equal size. Sagittal constriction smaller than the transverse. Surface of the disk bristly.

Dimensions.—Radius of the anterior arms 0.4, of the posterior 0.5; longitudinal constriction 0.3, transverse 0.35.

Habitat.—North Pacific, Station 253, surface.

11. Myelastrum rotula, n. sp.

Anterior arms little broader than the posterior, but of the same length. Each arm four-lobed, with three terminal deep incisions of equal size. Sagittal and transverse constrictions equal. The whole disk nearly circular, resembles a wheel with sixteen spokes. Surface smooth.

Dimensions.—Radius of all four arms 0.5; longitudinal and transverse constrictions 0.3.

Habitat.—Pacific, central area, Station 274, surface.

12. Myelastrum giganteum, n. sp.

Anterior arms somewhat broader and shorter than the posterior. Each arm four-lobed, with three shallow terminal incisions, the middle incision twice as deep as the two laterals. Sagittal constriction a little larger than the transverse. Margin ciliated, with radial bristle-shaped spines as prolongations of the inner radial beams, proceeding from the central disk (as in Myelastrum dodecaceros, Pl. 47, figs. 11, 11a).

Dimensions.—Radius of the anterior arms 0.6, of the posterior 0.8; longitudinal constriction 0.6, transverse 0.5.

Habitat.—Pacific, central area, Station 271, surface.

13. Myelastrum anomalum, n. sp. (Pl. 47, fig. 9).

All four arms of different size and form; anterior arms broader, posterior longer; one anterior arm trifid, the three other arms bifid; length of the branches unequal; all four angles between the arms unequal. (This anomalous form, seen only once, may be an individual abnormality.)

Dimensions.—Radius of the arms 0.4 to 0.7; constrictions 0.3.

Habitat.—North Pacific, Station 237, surface.

Genus 240. Pentalastrum,^[279] Haeckel, 1881, Prodromus, p. 461.

Definition.—Porodiscida with five simple, undivided, chambered arms, without a patagium.

The genus Pentalastrum opens the small series of Euchitonida, in which the shell is not provided with three or four arms, as usual, but with five. All forms of this little group are rare. Some species resemble in their external form and in the articulation of their arms certain forms of Asterida. In Pentalastrum, the most simple genus, the five arms are simple, not forked, and without a patagium. It can be derived from Dictyastrum or Stauralastrum by increase of the number of arms.

Subgenus 1. Pentalastrella, Haeckel.

Definition.—All five arms equal, with equal angles between them. Shell a regular pentagon.

1. Pentalastrum asteracanthion, n. sp.

All five arms equal, club-shaped, at their thickened obtuse end three times as broad as at their base, twice as long as broad. Angles between the arms equal.

Dimensions.—Radius of each arm 0.2, basal breadth 0.03, distal breadth 0.08.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

2. Pentalastrum astropecten, n. sp.

All five arms equal, with five to six distinct, simple joints, the basal joint two-thirds as broad as the terminal joint, which bears a strong conical spine. Angles between the arms equal. (Resembles Pentinastrum asteriscus, Pl. 44, fig. 2, but has no patagium.)

Dimensions.—Radius of each arm 0.14, basal breadth 0.024, distal breadth 0.036.

Habitat.—Pacific, central area, Station 263, depth 2650 fathoms.

Subgenus 2. Pentalastromma, Haeckel.

Definition.—Arms of different sizes, one odd arm larger than the two others; the opposite odd angle generally different from the four other angles.

3. Pentalastrum ophidiaster, n. sp. (Pl. 44, fig. 3).

Arms nearly triangular, at their obtuse truncated distal end twice as broad as at their base. Four arms equal, with five joints each; the fifth arm twice as long, with seven joints. Angles between the arms nearly equal; the odd angle a little larger.

Dimensions.—Radius of the larger odd arm 0.25, of the four smaller arms 0.15; basal breadth 0.035, distal breadth 0.07.

Habitat.—Pacific, central area, Station 274, surface.

4. Pentalastrum cometa, n. sp.

Arms nearly cylindrical, at their obtuse truncated distal end one and a half times as broad as at their base. Posterior odd arm very large, with eleven joints, about three times as long as the two lateral arms (with five joints each) and four times as long as the two anterior arms (with three joints each). Angles between the paired arms different; the two lateral angles smaller than the two posterior, and these smaller than the odd anterior angle.

Dimensions.—Radius of the odd posterior arm 0.5, of the lateral arms 0.25, of the anterior arms 0.18; basal breadth 0.05, distal breadth 0.08.

Habitat.—South Pacific, Station 288, surface.

Genus 241. Pentinastrum,^[280] Haeckel, 1881, Prodromus, p. 461.

Definition.—Porodiscida with five simple, undivided, chambered arms, connected by a patagium.

The genus Pentinastrum differs from the foregoing Pentalastrum only in the development of a patagium or connecticulum between the arms, and bears therefore the same relation to it that Histiastrum does to Stauralastrum, or Hymeniastrum to Dictyastrum.

1. Pentinastrum asteriscus , n. sp. (Pl. 44, fig. 2).

All arms equal, twice as long as broad, at their base two-thirds as broad as at their truncated distal end, which bears a strong, pyramidal, terminal spine. Each arm is divided by five transverse septa into six joints or chambers, and each of these by a radial beam into a pair of chambers. The five radial beams arise from the innermost chamber of the central disk, and end in the five terminal spines. The diameter of the central disk is larger than the length of the arms. The angles between the arms are equal and filled up by an incomplete patagium, so that the whole disk forms a regular pentagon with five concave sides.

Dimensions.—Radius of each arm (without terminal spine) 0.14; breadth at their base 0.02, at their terminal joint 0.03; radius of the central disk 0.06.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

2. Pentinastrum goniaster, n. sp.

? Stephanastrum sp., Bury, 1862, Polycystins of Barbados, pl. xx. fig. 1.

All five arms equal, four times as long as broad, club-shaped, at their globose distal end twice as broad as at their base, and armed with a strong conical terminal spine. Diameter of the central disk equals only one-third of the length of the arms. The articulation of the spongy arms is somewhat obscure. Patagium complete, totally fills up the interbrachial spaces, so that the whole disk forms a regular pentagon with five rectilinear sides, except that the terminal spines project at the corners.

Dimensions.—Radius of each arm 0.18, basal breadth 0.02, distal breadth 0.04; radius of the central disk 0.05.

Habitat.—South Pacific, Station 295, depth 1500 fathoms; also fossil in the rocks of Barbados.

Genus 242. Pentophiastrum,^[281] n. gen.

Definition.—Porodiscida with five forked chambered arms, without a patagium.

The genus Pentophiastrum differs from the two preceding genera by the bifurcation of the five arms, and can be derived either from Pentalastrum by the ramification of the distal ends of the arms, or from the similar Myelastrum by the increase in the number of arms.

1. Pentophiastrum dicranastrum, n. sp.

All five arms equal, with equal angles between them. Each arm in the basal half simple, in the distal half forked; both branches of it equal, with obtuse ends. (This regular species resembles Dicranastrum furcatum, Pl. 47, fig. 2, but with five rays instead of four; also the form of the arms is more slender and the edges smooth.)

Dimensions.—Radius of each arm 0.25, breadth 0.05.

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

Subgenus Pentophiastromma, Haeckel.

Definition.—Arms of different size, one odd arm opposite to the angle between both arm-pairs.

2. Pentophiastrum caudatum, n. sp. (Pl. 47, fig. 5).

Arms in pairs different; four arms in the basal half simple, in the distal half forked; the fifth (posterior) odd arm simple, undivided, cylindrical; the anterior pair a little smaller than the posterior; the neighboring branches of the two pairs on each side larger than the two others. Axes of the arms and their branches straight.

Dimensions.—Radius of the arms about 0.5, breadth 0.12.

Habitat.—North Atlantic, Station 353, depth 2965 fathoms.

3. Pentophiastrum forcipatum, n. sp. (Pl. 47, fig. 4).

Arms in pairs different, all in the basal two thirds simple, in the distal third forked. Only in the posterior (odd) arm both branches are equal, in the four others unequal. The common axis of the posterior lateral pair is horizontal, perpendicular to the median line; the axes of the anterior pair are pincer-like, concavely curved towards the median line or principal axis.

Dimensions.—Radius of the arms about 0.5, breadth 0.14.

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

Genus 243. Hexalastrum,^[282] Haeckel, 1881, Prodromus, p. 461.

Definition.—Porodiscida with six simple chambered arms, without a patagium.

The genus Hexalastrum, together with the following Hexinastrum, encloses those Euchitonida in which the number of the chambered arms surrounding the central disk amounts to six. This is the highest number of these articulated marginal appendages which is reached in any Discoidea. Formerly (1881) in my Prodromus, p. 459, I supposed that the same number was reached also by one Coccodiscid, and called this genus Hexactura. Afterwards I was convinced that this form was also a Hexalastrum.

1. Hexalastrum palmanthum, n. sp.

All six arms equal, with equal angles between them. Each arm club-shaped, three times as long as broad, twice as broad at the thickened distal end as at the base, without a terminal spine.

Dimensions.—Radius of each arm 0.2, basal breadth 0.02, distal breadth 0.06.

Habitat.—Pacific, central area, Station 274, depth 2750 fathoms.

2. Hexalastrum crinanthum, n. sp.

All six arms equal, with equal angles between them. Each arm club-shaped, four times as long as broad, at the egg-shaped distal end three times as broad as in the linear basal part, provided with numerous short conical spines and one longer terminal spine. (Resembles Stauralastrum rhopalophorum, Pl. 45, fig. 1, but with six rays instead of four.)

Dimensions.—Radius of each arm 0.3, basal breadth 0.03, distal breadth 0.08.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

Subgenus Hexalastromma, Haeckel.

Definition.—Arms more or less different in size or form; shell bilateral.

3. Hexalastrum orchidaceum, n. sp. (Pl. 44, fig. 5).

Hexactura orchidacea, Haeckel, 1881, Prodromus, p. 459.

Arms different in length, so that two unequal opposite odd arms determine the main axis, and the four other arms lie on both sides of this as two different pairs. The proportion of their relative length is the following:—anterior lateral arms five, anterior odd arm six; posterior lateral arms seven, posterior odd arm eight. Each arm is club-shaped, two to three times as long as broad, and divided into six to eight joints by five to seven transverse septa; its distal end is armed with a terminal spine and twice as broad as its base.

Dimensions.—Radius of the posterior odd arm 0.4, of the anterior odd arm 0.3; of the posterior lateral pair 0.35, of the anterior lateral pair 0.25; basal breadth 0.08, distal breadth 0.16.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

Genus 244. Hexinastrum,^[283] Haeckel, 1881, Prodromus, p. 461.

Definition.—Porodiscida with six simple, undivided, chambered arms, connected by a patagium.

The genus Hexinastrum differs from its ancestral form Hexalastrum by the development of a patagium between the arms. The only observed species is regular.

1. Hexinastrum geryonidum, n. sp. (Pl. 44, fig. 4).

Hexalastrum geryonidum, Haeckel, 1879, Atlas (pl. xliv. fig. 4).

Disk quite regular with six radii; all six arms of the same size and form, at their broad, convexly rounded, smooth end five times as broad as at their narrow base, and little longer than broad. Each arm is divided by eight transverse septa into nine simple joints or chambers of the same height; the breadth of the distal chambers increases rapidly. The regular, hexagonal, central disk exhibits four concentric rings around the central chamber. Patagium between the arms incomplete, with concavely fluted edge.

Dimensions.—Radius of each arm 0.15, basal breadth 0.016, distal breadth 0.08; radius of the central disk 0.04.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

Family XXII. Pylodiscida, n. fam. (Pl. 48, figs. 12-20).

Definition.—Discoidea without phacoid shell, with flat discoidal shell, in which a simple spherical central chamber is surrounded by one or two concentric triradial girdles; each girdle with three gates, separated by three simple arm-chambers. Surface of the disk with three open or latticed gates on each flat side.

The family Pylodiscida represents a new small but interesting group of Discoidea, which exhibits rather complex affinities to different groups of Sphærellaria. In my Prodromus (1881, p. 464) I had enumerated only two genera of this family, Triopyle and Hexapyle, and had united them with Tetrapyle and allied genera in the family Pylonida. Indeed, the resemblance of skeletal structure in the two groups is very great. The most simple forms of both groups exhibit a simple spherical latticed central chamber, which is surrounded by few latticed chambers of similar size and form, separated by open gates. But in the Pylonida these chambers are opposite in pairs, and form together a complete lattice-girdle around the central chamber, whereas in the Pylodiscida the chambers are not opposite in pairs in one axis, and form therefore only latticed half girdles, which arise from the central chamber like radial arms, and may perhaps better be called "arm-chambers"; their number is constantly three. The free open spaces between these three arm-chambers form three gates, comparable to the two or four gates of Amphipyle, Tetrapyle, &c., and become afterwards closed by lattice-work in a similar way in both groups. A more important difference between them is indicated by the further mode of growth. The Pylonida build new girdles in all three dimensive planes (alternating in the transverse, lateral and sagittal planes); their geometric fundamental form is therefore the "lentellipsis" or the "triaxial ellipsoid." The Pylodiscida, however, grow only at the periphery of the discoidal shell in one single plane (the equatorial plane); their fundamental form is therefore the biconvex lens or the flat disk (a shortened cylinder). This important difference is my deciding motive, in separating the latter from the former and in regarding the Pylodiscida as true Discoidea, the more so as they can easily be derived from Archidiscus, the fundamental and ancestral form of the Porodiscida.

One single form of Archidiscus seems to be of peculiar importance in this relation, viz., Archidiscus hexoniscus (Pl. 48, fig. 10). In this species the simple central chamber is surrounded by a latticed ring or girdle, composed of six equal chambers of the same size and form, all lying in the same plane with the central chamber. In a nearly allied species, viz., Archidiscus pyloniscus, the six ring-chambers are different, three smaller (with denser network) alternating with three larger (of looser network); if we imagine the network of the latter reduced to a marginal bar we get Triopyle, and if also this bar disappear by reduction we get Triolena, the most simple form of the Pylodiscida. Even Archidiscus pyloniscus may possibly represent the same form among the Porodiscida as Triodiscus lenticula among the Pylodiscida; this important form indicates clearly the close affinity of the two families.

If we take the latter, nearly identical form as the common starting point of both families of Cyclodiscaria, then probably Triopyle and Triolene must be regarded as retrograde forms, derived from Triodiscus in the one case, from Archidiscus in the other, by reduction of three interradial arm-chambers, whilst three perradial only remain. But it is also possible that the most simple form, Triolene, originated independently from some Cenosphæra, three simple radial chambers, like the latticed central chamber, being derived from the latter by apposition in three equidistant radii, whilst three other radii between them remained free. In this case the other genera of Pylodiscida are derived from their ancestral form Triolene.

Adopting this latter view, we find that all eight genera of Pylodiscida, here distinguished, may be regarded as following members of a continuous series. If the three simple arm-chambers of Triolene, surrounding the equal central chamber, become united at their distal ends by a concentric equatorial ring, then originates Triopyle; and this graduates into Triodiscus by fenestration of the three open gates between the three latticed arms. Whilst these three genera form together the subfamily Triopylida, a second family, Hexapylida, is composed of three other analogous genera, in which the same process of development becomes repeated.

Pylolena, the most simple form of Hexapylida, arises from Triodiscus by the development of three new arm-chambers (of the second order) which are apposed at the distal end of the three primary arm-chambers (of the first order) in the same radius. If the distal ends of these three secondary arm-chambers become united by a concentric latticed ring or girdle, we get Hexapyle (with six open gates, two in each radius), and if its six gates become afterwards closed by loose lattice-work, we arrive at Pylodiscus (a repetition of Triodiscus).

A third subfamily, Discopylida, is formed by the building of a chambered equatorial girdle around the margin of Pylodiscus. This girdle has quite the same structure as the similar chambered rings or girdles of the Porodiscida and Coccodiscida. Between the two sieve-plates of the disk surface is enclosed a variable number (twelve to twenty-four or more) of chambers, imperfectly separated by radial beams, which connect the margin of the Pylodiscus-shell with an outer peripheral concentric ring. In Discozonium this marginal ring is perfect, whilst in Discopyle it is interrupted by a peculiar large opening, a "marginal osculum" surrounded by a corona of spines, quite the same remarkable formation which we encountered in Ommatodiscus among the Porodiscida.

All Pylodiscida are therefore triradial (with three perradial arms and three interradial gates between them), and many of them have a great resemblance to certain triradial Porodiscida and Spongodiscida, perhaps not only a morphological resemblance, but also a true phylogenetic relation. But it is remarkable that we do not find further forms of development in this family, by multiplication either of the arm-chambers (further growth in the three perradii) or of the concentric chambered rings (in the periphery of the disk margin).

The central capsule of the Pylodiscida is constantly flat, discoidal, and enclosed between the two sieve-plates of the surface. Its form is either circular or triangular.

Synopsis of the Genera of the Pylodiscida.

I. Subfamily Triopylida. Three gates between three simple arm-chambers. Three gates open, without a barring equatorial girdle, 245. Triolena.

Three gates barred by a latticed equatorial girdle. Gate-faces simple, 246. Triopyle.

Gate-faces latticed, 247. Triodiscus.

II. Subfamily Hexapylida. Six gates between three double arm-chambers (three inner and three outer); no chambered marginal girdle. Three outer gates open, without a barring equatorial girdle, 248. Pylolena.

Three outer gates barred by a latticed (second) equatorial girdle. Both faces of the outer gates simple, 249. Hexapyle.

Both faces of the outer gates latticed, 250. Pylodiscus.

III. Subfamily Discopylida. Six gates between three double arm-chambers. In the equatorial plane on the margin of the Pylodiscus-shell is a chambered equatorial girdle. No peculiar osculum on the margin of the disc, 251. Discozonium.

One peculiar osculum (with a corona of spines) on the margin of the disc, 252. Discopyle.

I. Subfamily Triopylida. Three gates between three simple arm-chambers.

Three gates open, without a barring equatorial girdle,

245. Triolena.

Three gates barred by a latticed equatorial girdle.

Gate-faces simple,

246. Triopyle.

Gate-faces latticed,

247. Triodiscus.

II. Subfamily Hexapylida. Six gates between three double arm-chambers (three inner and three outer); no chambered marginal girdle.

Three outer gates open, without a barring equatorial girdle,

248. Pylolena.

Three outer gates barred by a latticed (second) equatorial girdle.

Both faces of the outer gates simple,

249. Hexapyle.

Both faces of the outer gates latticed,

250. Pylodiscus.

III. Subfamily Discopylida. Six gates between three double arm-chambers.

In the equatorial plane on the margin of the Pylodiscus-shell is a chambered equatorial girdle.

No peculiar osculum on the margin of the disc,

251. Discozonium.

One peculiar osculum (with a corona of spines) on the margin of the disc,

252. Discopyle.

Subfamily 1. Triopylida, Haeckel.

Definition.—Pylodiscida with a simple, spherical or lenticular, central chamber, surrounded by three simple arm-chambers, which are separated by three notches or gates.

Genus 245. Triolena,^[284] n. gen.

Definition.—Pylodiscida with a simple, spherical or lenticular, central chamber, surrounded by three simple arm-chambers. Notches between the three arms open.

The genus Triolena is the most simple form of all Pylodiscida, and must be regarded as their common ancestral form, from an ontogenetic as well as a phylogenetic point of view. The small shell is composed of a simple, spherical or lenticular, latticed, central chamber, and of three simple, surrounding equal arms, which are also simple latticed chambers, lie in the equatorial plane, and are separated by three equal angles or open gates.

1. Triolena primordialis, n. sp. (Pl. 48, fig. 12).

Arm-chambers trapezoid, nearly square, of the same size as the circular, lenticular, primordial, central chamber. Surface of the disk smooth.

Dimensions.—Diameter of the shell 0.045, of the central chamber 0.015, of each arm 0.015.

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

2. Triolena tribelone, n. sp.

Arm-chambers lanceolate, of the same breadth as and twice the length of the triangular, central chamber; at the pointed end of each arm is a conical terminal spine (in the equatorial plane). Surface of the disk thorny.

Dimensions.—Diameter of the shell 0.05, of the central chamber 0.015; length of the arms 0.02, breadth 0.016.

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

3. Triolena trispinosa, n. sp.

Arm-chambers ovate, in the basal half nearly as broad as the hexagonal central chamber, at the pointed distal end with a strong conical radial spine of double the length. Surface rough.

Dimensions.—Diameter of the shell 0.055, of the central chamber 0.02.

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

4. Triolena hexabelone, n. sp.

Arm-chambers nearly triangular, at the base half as broad as the hexagonal central chamber, at the truncate distal end one and a half times as broad, and armed with two radial conical spines (in the equatorial plane). Surface of the disk smooth.

Dimensions.—Diameter of the shell 0.06, of the central chamber 0.02.

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

5. Triolena trigonalis, n. sp.

Arm-chambers nearly triangular, at the base half as broad as the circular central chamber, at the concave lunulate distal end twice as broad, and armed with four conical radial spines (two on each side of the equatorial plane). Surface thorny.

Dimensions.—Diameter of the shell 0.05, of the central chamber 0.015.

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

Genus 246. Triopyle,^[285] Haeckel, 1881, Prodromus, p. 464.

Definition.—Pylodiscida with a simple, spherical or lenticular, central chamber, surrounded by three simple arm-chambers. Notches between the three arms transformed into gates by a connecting equatorial girdle.

The genus Triopyle differs from the preceding Triolene in the development of a simple ring or latticed equatorial girdle, which connects the distal ends of the three arm-chambers, and transforms the open notches between them into three gates. The ring may be circular, triangular, or hexagonal.

1. Triopyle circulus, n. sp.

Disk circular, three times as broad as the hexagonal central chamber. Three arm-chambers trapezoidal, at the convex distal end as broad, at the base half as broad as the three circular gates between them. Surface smooth. No marginal spines on the girdle.

Dimensions.—Diameter of the disk 0.045, of the gates 0.015.

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

2. Triopyle hexagona, n. sp. (Pl. 48, fig. 13).

Disk hexagonal, three times as broad as the circular central chamber. Three arm-chambers trapezoidal, at the truncated distal end as broad, at the base half as broad as the three triangular gates between them. Surface smooth. No marginal spines.

Dimensions.—Diameter of the disk 0.05, of the gates 0.02.

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

3. Triopyle trigona, n. sp.

Disk triangular, four times as broad as the circular central chamber. Three arm-chambers nearly triangular, at the narrow base half as broad, at the distal end twice as broad as the circular or roundish gates. Surface smooth. On the margin (in the equatorial plane) three strong pyramidal spines (at the end of the arms).

Dimensions.—Diameter of the disk 0.04, of the gates 0.015.

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

4. Triopyle cordigera, n. sp.

Disk hexagonal, four times as broad as the hexagonal central chamber. Three arm-chambers triangular, at the base half as broad as at the truncated distal end, about the same size as the three heart-shaped gates. On the six corners of the margin (which forms a regular hexagon) are six pyramidal radial spines, as prolongations of the arm-edges.

Dimensions.—Diameter of the disk 0.05, of the gates 0.02.

Habitat.—Indian Ocean, Ceylon, surface, Haeckel.

5. Triopyle renigera, n. sp.

Disk hexagonal, five times as broad as the circular central chamber. Three arm-chambers trapezoidal, at the base one-third, at the distal end two-thirds as broad as the three kidney-shaped gates. On the six corners of the margin (which forms an irregular hexagon) six conical radial spines, as prolongations of the arm-edges.

Dimensions.—Diameter of the disk 0.06, of the gates 0.02.

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

6. Triopyle spinigera, n. sp.

Disk roundish, triangular, four times as broad as the triangular central chamber, which is armed with three radial spines between the arms. Arm-chambers club-shaped, at the narrow base one-fourth, at the distal end half as broad as the square gates. On the margin twelve large conical spines, two opposite on each face of the distal end of each arm-edge. Three smaller radial spines on the three corners of the girdle (in the same interradial meridian planes as the three spines of the central chamber). Compare Triodiscus spinosus.

Dimensions.—Diameter of the disk 0.05, of the gates 0.02.

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

Genus 247. Triodiscus,^[286] n. sp.

Definition.—Pylodiscida with a simple, spherical or lenticular, central chamber, surrounded by three simple arm-chambers. Notches between the three arms closed by lattice-work and by an equatorial girdle.

The genus Triodiscus differs from the preceding Triopyle in the development of loose lattice-work on both sides of the discoidal shell. This network closes the gates and transforms the whole shell into a fenestrated lens. The singular species of Triodiscus correspond to certain species of Triopyle.

1. Triodiscus lenticula, n. sp.

Disk circular, lenticular, three times as broad as the central chamber. Three arm-chambers trapezoidal, of the same size and form as the three gates between them, which are closed by a loose delicate network (differs from Triopyle circulus by the production of the two convex latticed plates, which envelop the whole lens). Margin smooth.

Dimensions.—Diameter of the disk 0.045, of the gates 0.015.

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

2. Triodiscus trigonus, n. sp.

Disk triangular, four times as broad as the central chamber. Three arm-chambers at the base half as broad, at the distal end twice as broad as the roundish gates. Surface smooth. On the three corners of the margin (in the arm-radius) three strong spines. (Differs from Triopyle trigona only in the loose framework closing the gates.)

Dimensions.—Diameter of the disk 0.04, of the gates 0.015.

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

3. Triodiscus spinosus, n. sp. (Pl. 48, fig. 14).

Disk subcircular, four times as broad as the triangular central chamber. Three arm-chambers club-shaped, at the base one-third, at the distal end two-thirds as broad as the semicircular gates. Surface thorny. On the margin fifteen larger radial spines, three on the corners of the disk (in the radius of the gates), twelve on the two faces of the arms ends (two opposite on the edge of each end.) (Differs from Triopyle spinigera mainly by the delicate hexagonal network closing the gates.)

Dimensions.—Diameter of the disk 0.05, of the gates 0.02.

Habitat.—North Atlantic, Canary Islands (Lanzerote, Haeckel).

Subfamily 2. Hexapylida, Haeckel.

Definition.—Pylodiscida with triopyle-shaped medullary shell, surrounded by three distal arm-chambers, which are separated by three open notches or gates.

Genus 248. Pylolena,^[287] n. gen.

Definition.—Pylodiscida with triopyle-shaped medullary shell, surrounded by three distal arm-chambers. Notches between the three arms open.

The genus Pylolena opens the series of the Hexapylida, or of those Pylodiscida in which the centre of the shell is formed by a tri-radiated medullary shell like Triopyle. In the equatorial plane of this triopyle-shaped disk are developed on its margin three distal arm chambers, as prolongations of the three arms of Triopyle, but much larger. In Pylolene the three angles or notches between the distal arms remain open, repeating the form of Triolene.

1. Pylolena inermis, n. sp.

Arms club-shaped, at the base half as broad, at the rounded distal end as broad as the triopyle-shaped medullary shell. Surface and margin smooth.

Dimensions.—Diameter of the cortical shell 0.15, of the medullary shell 0.05.

Habitat.—Equatorial Atlantic, Station 347, surface; Central Pacific, Station 272, surface.

2. Pylolena armata, n. sp. (Pl. 48, fig. 15).

Arms trapezoid, at the base half as broad, at the distal end twice as broad as the triopyle-shaped medullary shell. Surface and margin thorny. Twelve strong conical spines at the distal end of the three arms, two opposite on both faces of the arm-edges.

Dimensions.—Diameter of the cortical shell 0.2, of the medullary shell 0.06.

Habitat.—South Atlantic, Station 325, surface.

Genus 249. Hexapyle,^[288] Haeckel, 1881, Prodromus, p. 464.

Definition.—Pylodiscida with triopyle-shaped medullary shell, surrounded by three distal arm-chambers. Notches between the three arms transformed into gates by a connecting equatorial girdle.

The genus Hexapyle differs from the preceding Pylolene in the development of an equatorial ring or latticed girdle, which connects the free extremities of the three distal ends and transforms the open notches between them into gates. It simulates therefore the formation of Triopyle, from which it differs by duplication of the arm-joints and of the gates (in each radius occur one proximal and one distal gate).

1. Hexapyle triangula, n. sp.

Cortical shell triangular, with three rounded corners, three times as broad as the triangular triopyle-shaped medullary shell. Surface smooth or rough, but not spiny. Three arms two-thirds as broad as the three egg-shaped gates of each side.

Dimensions.—Diameter of the cortical shell (or length of one side of the triangle) 0.15, of the medullary shell 0.05; breadth of the gates 0.06, of the bridges between them 0.04.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

2. Hexapyle sexangula, n. sp.

Cortical shell hexagonal, with six equal sides, four times as broad as the triangular triopyle-shaped medullary shell. Surface rough, but not spiny. Three arms (on their smallest part) half as broad as the three triangular gates (on their broadest part).

Dimensions.—Diameter of the cortical shell 0.16, of the medullary shell 0.04; breadth of the gates 0.06, of the bridges 0.03.

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

3. Hexapyle circularis, n. sp.

Cortical shell circular, four times as broad as the triangular, Triopyle-shaped medullary shell. Surface smooth. Three arms half as broad as the three kidney-shaped gates on each side of the shell.

Dimensions.—Diameter of the cortical shell 0.2, of the medullary shell 0.05; breadth of the gates 0.08, of the bridges between them 0.04.

Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.

4. Hexapyle triacantha, n. sp.

Cortical shell triangular, thorny, with three pointed corners, prolonged into three strong conical radial spines; its diameter four times as great as that of the medullary shell. Three arms of the same breadth as the three egg-shaped gates of each side.

Dimensions.—Diameter of the cortical shell (or length of one side of the triangle, without spines) 0.2, of the medullary shell 0.05; breadth of the gates and of the bridges between them 0.06.

Habitat.—Indian Ocean, surface; Madagascar, Rabbe.

5. Hexapyle hexacantha, n. sp.

Cortical shell hexagonal, thorny, three times as broad as the medullary shell. Six stronger conical radial spines on the six corners at equal distances, lying in the equatorial plane of the disk. Three half girdles half as broad as the three triangular gates of each side.

Dimensions.—Diameter of the cortical shell 0.15, of the medullary shell 0.05; breadth of the gates 0.05, of the bridges 0.025.

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

6. Hexapyle dodecantha, n. sp. (Pl. 48, fig. 16).

Cortical shell triangular, thorny, with rounded corners, three and a half times as broad as the medullary shell. Twelve stronger radial spines, six opposite in pairs on each side of the discoidal shell, as prolongations of the lateral edges of the triangular gates, which are about the same breadth as the half girdles between them.

Dimensions.—Diameter of the cortical shell 0.21, of the medullary shell 0.06; breadth of the gates and of the bridges 0.06.

Habitat.—Pacific, central area, Station 270, surface.

7. Hexapyle polyacantha, n. sp.

Cortical shell circular, thorny, with a circle of numerous conical radial spines in the periphery; its diameter nearly three times as great as that of the medullary shell. Three half-girdles half as broad as the three kidney-shaped gates on each side of the discoidal shell.

Dimensions.—Diameter of the cortical shell 0.11, of the medullary shell 0.04; breadth of the gates 0.04, of the bridges between them 0.02.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

Genus 250. Pylodiscus,^[289] n. gen.

Definition.—Pylodiscida with Triopyle-shaped medullary shell, surrounded by three distal arm-chambers. Notches between the three arms closed by lattice-work and by an equatorial girdle.

The genus Pylodiscus differs from Hexapyle in the development of two convex plates of lattice-work, which close the six open gates and transform the disk into a biconvex fenestrated lens. Pylodiscus simulates therefore the characteristic form of Triodiscus; but whilst in the latter we find only three arm-joints and three simple gates, their number is doubled in the former.

1. Pylodiscus triangularis, n. sp. (Pl. 48, fig. 17).

Cortical shell triangular, with rounded corners, three times as broad as the triangular, Triopyle-shaped medullary shell. Three arms about as broad as the three egg-shaped gates between them. (Differs from Hexapyle triangula only by the delicate network of both triangular convex covering plates, which close the open gates.) Six larger and many smaller spines on the margin of the disk.

Dimensions.—Diameter of the disk 0.15, of the gates 0.05.

Habitat.—Pacific, central area, Station 270, depth 2925 fathoms.

2. Pylodiscus sexangularis, n. sp.

Cortical shell hexangular, equilateral, four times as broad as the circular, Triopyle-shaped medullary shell. Surface spiny. Three arms nearly of the same form and size as the three triangular gates between them. (Similar to Hexapyle sexangularis, but differing in the irregular loose network closing the gates.)

Dimensions.—Diameter of the disk 0.18, of the gates 0.06.

Habitat.—North Pacific, south of Japan, Station 237, surface

3. Pylodiscus cardiopylus, n. sp.

Cortical shell hexangular, equilateral, five times as broad as the triangular, Triopyle-shaped medullary shell. Surface smooth. Three arms triangular, at the distal end as broad as the three heart-shaped gates. On the margin six strong pyramidal spines in the equatorial plane (adradial, as prolongations of the lateral arm-edges).

Dimensions.—Diameter of the disk 0.15, of the gates 0.05.

Habitat.—Indian Ocean, Sunda Strait, Rabbe.

4. Pylodiscus nephropylus, n. sp.

Cortical shell circular, three times as broad as the circular, Triopyle-shaped medullary shell. Surface spiny. Three arms trapezoidal, half as broad as the three kidney-shaped gates. On the margin twelve stronger, conical, radial spines, opposite in pairs on both sides of the disk, disposed in six pairs at the distal end of the arms.

Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.06.

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

Subfamily 3. Discopylida, Haeckel.

Definition.—Pylodiscida with Triopyle-shaped medullary shell and Pylodiscus-shaped cortical shell, which is surrounded by a marginal chambered equatorial girdle.

Genus 251. Discozonium,^[290] n. gen.

Definition.—Pylodiscida with Triopyle-shaped medullary shell and Pylodiscus-shaped cortical shell, which is surrounded by an equatorial chambered girdle. No peculiar osculum on the margin of the disk.

The genus Discozonium and the following Discopyle make up together the small group of the Discopylida, or those Pylodiscida in which a discoidal shell like Pylodiscus is surrounded by a marginal equatorial girdle; this girdle is divided into twelve to twenty-four or more chambers by radial beams, which are the external prolongations of the radial marginal spines of Pylodiscus. The latter genus bears therefore to Discozonium the same relation as Sethodiscus in the other Discoidea does to Lithocyclia, or Phacodiscus to Coccodiscus.

1. Discozonium cyclonium, n. sp.

Disk circular, lenticular, with smooth margin, three times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell kidney-shaped, twice as broad as the three arms. Chambered equatorial girdle with twenty to twenty-four subregular chambers (similar to Discopyle osculata, Pl. 48, fig. 19, but without any marginal osculum).

Dimensions.—Diameter of the disk 0.2, of the cortical shell 0.14, of the medullary shell 0.07.

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

2. Discozonium trigonium, n. sp.

Disk triangular, with thorny margin, four times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell egg-shaped, scarcely as broad as the three arms. Chambered equatorial girdle with twenty-four to thirty irregular chambers.

Dimensions.—Diameter of the disk 0.24, of the cortical shell 0.2, of the medullary shell 0.06.

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

3. Discozonium hexagonium, n. sp. (Pl. 48, fig. 18).

Disk hexagonal, with spiny margin, four times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell kidney-shaped, one and a half times as broad as the arms. Chambered equatorial girdle with twelve large regular chambers; the radial beams between them are prolonged into twelve strong pyramidal marginal spines (three perradial on the ends of the arms, three interradial on the radii of the gates, six adradial between the former and latter).

Dimensions.—Diameter of the disk 0.2, of the cortical shell 0.12, of the medullary shell 0.05.

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

Genus 252. Discopyle,^[291] n. gen.

Definition.—Pylodiscida with Triopyle-shaped medullary shell and Pylodiscus-shaped cortical shell, which is surrounded by an equatorial chambered girdle. One peculiar osculum, surrounded by a corona of spines, on the margin of the disk.

The genus Discopyle differs from the preceding genus Discozonium in the development of a peculiar marginal osculum, and bears therefore to it the same relation as, in the Porodiscida, Ommatodiscus does to Porodiscus (compare above, p. 500). This peculiar osculum is here also surrounded by a corona of spines, and serves probably for the exit or outlet of a bunch of pseudopodia or a "sarcode-flagellum." Only two species of Discopyle have been observed, which represent perhaps better two different genera; in one species the disk is circular, in the other elliptical. In this latter the osculum lies on one pole of the main axis.

1. Discopyle osculata, n. sp. (Pl. 48, fig. 19).

Disk circular with spiny margin, three times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell kidney-shaped, on the inside with an interradial spine, twice as broad as the three pentagonal arms. Chambered equatorial girdle with twenty-four subregular chambers, in the radius of one odd gate with a large marginal osculum, which is as broad as the medullary shell, and surrounded by a dense corona of twenty to thirty strong conical spines.

Dimensions.—Diameter of the disk 0.15, of the cortical shell 0.1, of the medullary shell 0.05, of the marginal osculum 0.06.

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

2. Discopyle elliptica, n. sp. (Pl. 48, fig. 20).

Disk elliptical, four-fifths as broad as long, with spiny margin, three times as broad as the triangular, Triopyle-shaped medullary shell. Three gates of the cortical shell roundish, on the inside with an interradial spine, little broader than the quadrangular arms. Chambered equatorial girdle with twenty to thirty irregular chambers, on one pole of the main axis with a large marginal osculum, which is one-third as broad as the length of the main axis, and armed with a corona of twenty to thirty short conical spines. The osculum does not correspond to a certain radius.

Dimensions.—Diameter of the disk 0.15, of the cortical shell 0.08, of the medullary shell 0.04, of the marginal osculum 0.05.

Habitat.—Central Pacific, Station 267, depth 2700 fathoms.

Family XXIII. Spongodiscida, Haeckel (Pl. 41, fig. 11).

Definition.—Discoidea without a phacoid shell, with a flat discoidal shell, in which a simple spherical central chamber is surrounded by an irregular spongy framework (sometimes with concentric rings around the central chamber). Surface of the disk quite spongy, without porous sieve-plates.

The family Spongodiscida is the sixth and last family of the Discoidea, and bears to the other families of this group the same relation as the family Spongosphærida does to the other Sphæroidea, or the Spongurida to the other Prunoidea. Its characteristic structure consists in the irregular spongy framework of the disk, and mainly in the rough, irregular shape of its spongy surface, which is never covered with porous plates (neither phacoid shell nor corresponding sieve-plates), as in all other Discoidea. Of course a little spongy structure occurs also in many Porodiscida and even in some Coccodiscida (principally in the peripheral part of the disk or its chambered arms); but both flat (or convex) surfaces of the disk (at least in the central part) remain here constantly as simple lattice-plates, whilst in all Spongodiscida the whole surface of the disk is spongy.

When I constituted the family Spongodiscida in my Monograph (1862, pp. 452, 460) I had separated from them the Spongocyclida, exhibiting in the central part of the disk a more or less distinct concentric arrangement of the spongy chambers, whilst in the former the delicate spongy framework is quite irregular, composed of branched siliceous threads, connected and interwoven in all directions. But in all Spongocyclida the whole surface of the spongy disk is quite as irregularly rough and deprived of smooth sieve-plates as in all true Spongodiscida, and the more or less concentric structure of the central part of the disk in the former (very variable and often scarcely able to be recognised) seems not sufficient to separate both groups; even the single genera cannot be sufficiently separated by this character. I now therefore give up entirely the group of Spongocyclida (as already done in my Prodromus, 1881). Nevertheless the concentric annular structure in the dark central part of some Spongodiscida is very interesting as transition to the Porodiscida; it indicates already that the former are derived from the latter. Even the single genera in both families are corresponding.

In the new system of "Polycystina," which Ehrenberg gave, 1875 (Abhandl. d. k. Akad. d. Wiss. Berlin, p. 157), are enumerated under the Calodictya four genera "with spongy disk," viz., Spongodiscus, Rhopalodictyum, Dictyocoryne, Spongaster. Indeed these four genera, which I here retain, are true Spongodiscida, and must be separated from the other Calodictya, the greater part of which are Porodiscida. The number of species of true Spongodiscida now amounts to sixty-seven, which I dispose in thirteen genera.

The whole family may be divided into three subfamilies. The first of these are the Spongophacida (corresponding to the Trematodiscida among the Porodiscida), in which the circular margin of the spongy disk bears no radial appendages; either the margin is quite simple, spongy (Spongodiscus), or surrounded by a hyaline, solid, or porous equatorial girdle (Spongophacus). The disk is either more lenticular (biconvex) or more flat discoidal (a shortened cylinder), rarely a little biconcave (thicker at the margin than in the centre). The spongy framework of the solid disk is either quite irregular (Spongodisculus), or in the central part with concentric circular rings (Spongocyclia), or in the central part spirally convoluted (Spongospira).

The second subfamily, Spongotrochida, corresponds to the Stylodictyida (among the Porodiscida), and is distinguished by solid radial spines on the margin of the disk, disposed in the equatorial plane either irregularly or regularly (after the same order as in the other families of Discoidea).

The third subfamily, Spongobrachida, correspond perfectly to the Euchitonida (among the Porodiscida), bearing on the disk-margin two, three, or four spongy arms, commonly disposed regularly in the equatorial plane. Here also occurs the peculiar formation of a "patagium," or of an interbrachial spongy framework different from that of the arms, which connects the arms like a web-membrane in the equatorial plane.

The spongy framework exhibits in all these Spongodiscida no remarkable differences, being everywhere composed of fine branched solid siliceous threads, interwoven in all directions, with irregular meshes of very different size.

The central capsule of all Spongodiscida is filled up with the same spongy framework which covers also both its sides. It grows according to the enveloping skeleton, but remains constantly smaller. The form of the central capsule is circular (lenticular or discoidal) in the Spongophacida and Spongotrochida, whilst in the Spongobrachida it enters into the radial spongy arms, developed from the margin of the spongy disk.

Synopsis of the Genera of the Spongodiscida.

III. Subfamily Spongophacida. Spongy disk without radial appendages. Spongy disk with simple margin (without peculiar equatorial girdle), 253. Spongodiscus.

Spongy disk with a peculiar (solid or porous) equatorial girdle, 254. Spongophacus.

III. Subfamily Spongotrochida. Spongy disk with solid radial spines on the margin (in the equatorial plane). Few (two, three, or four) radial spines regularly disposed. Two opposite spines, 255. Spongolonche.

Three marginal spines, 256. Spongotripus.

Four crossed spines, 257. Spongostaurus.

Numerous (five to ten or more) radial spines, often irregularly disposed. Spines only on the margin (equatorial), 258. Stylotrochus.

Spines on both sides of the disk, 259. Spongotrochus.

III. Subfamily Spongobrachida. Spongy disk with spongy radial arms on the margin (in the equatorial plane). Two arms, opposite in one axis. Without a patagium, 260. Spongolena.

With a patagium, 261. Spongobrachium.

Three arms on the margin. Without a patagium, 262. Rhopalodictyum.

With a patagium, 263. Dictyocoryne.

Four arms in cross form. Without a patagium, 264. Spongasteriscus.

With a patagium, 265. Spongaster.

I. Subfamily Spongophacida. Spongy disk without radial appendages.

Spongy disk with simple margin (without peculiar equatorial girdle),

253. Spongodiscus.

Spongy disk with a peculiar (solid or porous) equatorial girdle,

254. Spongophacus.

II. Subfamily Spongotrochida. Spongy disk with solid radial spines on the margin (in the equatorial plane).

Few (two, three, or four) radial spines regularly disposed.

Two opposite spines,

255. Spongolonche.

Three marginal spines,

256. Spongotripus.

Four crossed spines,

257. Spongostaurus.

Numerous (five to ten or more) radial spines, often irregularly disposed.

Spines only on the margin (equatorial),

258. Stylotrochus.

Spines on both sides of the disk,

259. Spongotrochus.

III. Subfamily Spongobrachida. Spongy disk with spongy radial arms on the margin (in the equatorial plane).

Two arms, opposite in one axis.

Without a patagium,

260. Spongolena.

With a patagium,

261. Spongobrachium.

Three arms on the margin.

Without a patagium,

262. Rhopalodictyum.

With a patagium,

263. Dictyocoryne.

Four arms in cross form.

Without a patagium,

264. Spongasteriscus.

With a patagium,

265. Spongaster.

Subfamily 1. Spongophacida, Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with a simple circular disk, without radial appendages on the margin (neither solid spines nor chambered arms).

Genus 253. Spongodiscus,^[292] Ehrenberg, 1854, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 237.

Definition.—Spongodiscida with a simple circular disk, without radial appendages and without an equatorial girdle on the margin.

The genus Spongodiscus represents the most simple and primitive form of the Spongodiscida, or of those Discoidea in which the central disk is more or less spongy, composed of an irregular fine framework. In my Monograph (1862, pp. 452, 460, 469) I had separated the true Spongodiscus (first described by Ehrenberg, loc. cit.) and the Spongocyclia; the former being characterised by the irregular spongy framework of the whole disk, whilst in the latter this framework includes in the central part some concentric circular rings (approaching Porodiscus). In the same way afterwards Stöhr (1880, loc. cit.) separated the genus Spongospira as spongy disks, which include in the central part some spiral convolutions. But as these differences are rather inconstant and not sharply discernible, I think it now better to regard these three forms as subgenera of Spongodiscus. All three have the common simple circular disk, without any marginal appendages.

Subgenus 1. Spongodisculus, Haeckel.

Definition.—Spongy framework of the disk quite irregular, without concentric rings or spiral convolutions.

1. Spongodiscus mediterraneus, Haeckel.

Spongodiscus mediterraneus, Haeckel, 1862, Monogr. d. Radiol., p. 461, Taf. xii. figs. 14, 15.

Spongy disk plain on both sides, with quite an irregular framework, without concentric rings and without radial piercing beams. Texture everywhere uniform; meshes eight to ten times as broad as the bars.

Dimensions.—Diameter of the disk 0.08 to 0.24, of the meshes 0.005 to 0.008.

Habitat.—Mediterranean (Messina), Haeckel; also fossil in the Tertiary rocks of Sicily (Grotte), Stöhr.

2. Spongodiscus radiatus, n. sp.

Spongy disk plain on both sides, with quite irregular framework, without concentric rings, but with numerous piercing radial beams which are not prolonged into marginal spines. Texture everywhere uniform; meshes once and a half to twice as broad as the bars.

Dimensions.—Diameter of the disk 0.12 to 0.15, of the meshes 0.002 to 0.003.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

3. Spongodiscus resurgens, Ehrenberg.

Spongodiscus resurgens, Ehrenberg, 1854, Mikrogeol., Taf. xxxvB. B. iv., fig. 16.

Spongodiscus resurgens, Stöhr, 1880, Palæontogr., xxvi. p. 117, Taf. vi. fig. 11.

Spongy disk lenticular, biconvex, in the darker centre much thicker than towards the thin periphery, with an irregular framework, without concentric rings, but with numerous piercing radial beams. Texture equal; meshes three to four times as broad as the bars.

Dimensions.—Diameter of the disk 0.1 to 0.3, of the meshes 0.003 to 0.006.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific, surface; also fossil in the Tertiary rocks of Sicily and Barbados.

4. Spongodiscus favus, Ehrenberg.

Spongodiscus favus, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 301.

Spongy disk lenticular, biconvex, in the darker centre much thicker than towards the periphery, with an irregular framework, without concentric rings. Texture different, in the outer half with numerous radial beams and loose network, the meshes of which are three to four times as large as in the darker and denser framework of the centre.

Dimensions.—Diameter of the disk 0.2, of the outer meshes 0.008 to 0.012, of the inner meshes 0.002 to 0.003.

Habitat.—North Atlantic, Greenland, Færöe Channel (John Murray), surface.

5. Spongodiscus biconcavus, n. sp.

Spongy disk biconcave, in the peripheral, ring-like, thickened part twice as thick as in the hollowed central part, with an irregular framework, without concentric rings. Texture different, in the outer half looser than in the inner, darker part; meshes of the outer part five to six times, of the inner twice to three times, as broad as the bars.

Dimensions.—Diameter of the disk 0.25, of the outer meshes 0.01 to 0.012, of the inner 0.004 to 0.006.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Subgenus 2. Spongocyclia, Haeckel, 1862, Monogr. d. Radiol., p. 469.

Definition.—Spongy framework of the disk in the inner part with concentric, circular rings, in the outer part irregular.

6. Spongodiscus cycloides, Haeckel.

Spongodiscus cycloides, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 843.

Spongocyclia cycloides, Haeckel, 1862, Monogr. d. Radiol., p. 469, Taf. xxviii. fig. 1.

Spongy disk on both sides plain, in the central part with five to ten concentric, circular rings, in the peripheral part quite irregularly and densely spongy. Meshes twice to four times as broad as the bars.

Dimensions.—Diameter of the disk 0.1 to 0.2, of the meshes 0.003 to 0.006.

Habitat.—Mediterranean (Messina), North Atlantic (Canary Islands).

7. Spongodiscus spongocyclia, Haeckel.

Spongocyclia triangularis, Stöhr, 1880, Palæontogr., vol. xxvi. p. 119, Taf. vii. fig. 5.

Spongy disk lenticular, in the thicker central part with eleven to twelve circular, concentric rings, in the thinner, peripheral zone irregularly spongy. Meshes twice to four times as broad as the bars. (The triangular form in the specimen figured by Stöhr is accidental, produced by the broken margin.)

Dimensions.—Diameter of the disk 0.2 to 0.3, of the meshes 0.006 to 0.008.

Habitat.—Fossil in Tertiary rocks of Barbados (Haeckel) and Sicily (Stöhr).

Subgenus 3. Spongospira, Stöhr, 1880, Palæontogr., vol xxvi. p. 120.

Definition.—Spongy framework of the disk in the inner part with spiral convolutions, in the outer part irregular.

8. Spongodiscus florealis, Haeckel.

Spongospira florealis, Stöhr, 1880, Palæontogr., vol. xxvi. p. 120, Taf. vii. fig. 6.

Spongy disk lenticular, in the thicker central part with five to six spiral convolutions, in the outer peripheral zone irregularly spongy. No radial beams piercing the framework. Meshes three to four times as broad as the bars.

Dimensions.—Diameter of the disk 0.26, of the meshes 0.006 to 0.008.

Habitat.—Fossil in Tertiary rocks of Sicily (Grotte), Stöhr.

9. Spongodiscus spiralis, n. sp.

Spongospira spiralis, Haeckel, 1881, Prodromus.

Spongy disk on both sides plain, with twelve to sixteen spiral convolutions in the central part, with irregular, spongy framework in the outer part, pierced by numerous interrupted radial beams. Meshes five to six times as broad as the bars.

Dimensions.—Diameter of the disk 0.2 to 0.3, of the meshes 0.01 to 0.012.

Habitat.—Antarctic Ocean, Station 157, depth 1950 fathoms.

Genus 254. Spongophacus,^[293] Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with a simple circular disk, without radial appendages, on the margin surrounded by a thin porous or solid equatorial girdle.

The genus Spongophacus, represented hitherto only by a single but interesting species, differs from Spongodiscus by the peculiar girdle which surrounds the margin of the disk in the equatorial plane. It simulates the same formation as Perichlamydium in the Porodiscida, and resembles also Periphæna, &c., in the Phacodiscida.

1. Spongophacus periphæna, n. sp.

Spongy disk lenticular, with an irregular, dense framework, in the centre darker than in the peripheral part. Margin of the disk very thin, surrounded by a broad, circular girdle, lying in the equatorial plane, about as broad as the half radius of the spongy disk. The inner part of the girdle is perforated by numerous irregular, small pores, which pass over gradually into the spongy meshes; the outer part is quite homogeneous, solid, transparent, with an extremely thin margin.

Dimensions.—Diameter of the disk 0.2; breadth of the girdle 0.05.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

Subfamily 2. Spongotrochida, Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with a circular disk, the margin of which is armed with solid radial spines, situated in the equatorial plane (rarely also on both sides of the disk with radial spines).

Genus 255. Spongolonche,^[294] Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with two solid marginal spines, opposite in one equatorial diameter of the disk.

The genus Spongolonche opens the series of the Spongotrochida, or of those Spongodiscida in which the margin of the disk is armed with solid radial spines, situated in the equatorial plane. Spongolonche possesses only two such spines, opposite in one equatorial diameter of the disk; it corresponds therefore to Stylocyclia among the Coccodiscida, to Xiphodictya among the Porodiscida.

1. Spongolonche conostyla, n. sp..

Spongy disk circular, with irregular framework, without concentric rings. Both opposite radial spines conical, about as long as the radius of the disk, and four times as long as broad at the base. Margin of the disk nearly smooth.

Dimensions.—Diameter of the disk 0.16; length of the radial spines 0.18, basal thickness 0.045.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.

2. Spongolonche amphistyla, n. sp.

Spongy disk circular, with four to six concentric rings in the inner part, with quite an irregular framework in the outer part. Both opposite radial spines cylindrical, twice to three times as long as the diameter of the disk, at the base about as broad as two meshes of the framework. Margin of the disk ciliated.

Dimensions.—Diameter of the disk 0.2; length of the radial spines 0.4 to 0.6, basal thickness 0.01.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

Genus 256. Spongotripus,^[295] Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with three solid radial spines on the margin of the circular or triangular disk.

The genus Spongotripus is characterised by three marginal spines, which are commonly regularly disposed, more rarely in a bilateral or an irregular manner. It corresponds to Trigonocyclia among the Coccodiscida, to Tripodictya among the Porodiscida.

Subgenus 1. Spongotripodiscus, Haeckel.

Definition.—Radial spines of equal size and distance; triangle regular.

1. Spongotripus regularis, n. sp.

Spongy disk circular; three radial spines on its margin of equal size and equidistant, strong, conical, about as long as the diameter of the disk, and five times as long as broad at the base.

Dimensions.—Diameter of the disk 0.15; length of the spines 0.16, basal breadth 0.03.

Habitat.—Pacific, central area, Station 272, surface.

2. Spongotripus neumayri, Haeckel.

Spongechinus neumayri, Dunikowski, 1882, Denskchr. d. k. Akad. d. Wiss. Wien, xlv. p. 28, Taf. v. fig. 59.

Spongy disk circular, nearly spherical; three radial spines on its margin of equal size and equidistant, pyramidal, nearly as long as the diameter of the disk, and three times as long as broad at the base.

Dimensions.—Diameter of the disk 0.15 to 0.2; length of the spines 0.11, basal breadth 0.04.

Habitat.—Fossil in the Jura of the Alps and in Tertiary rocks of Barbados.

3. Spongotripus strepsiceros, n. sp.

Spongy disk circular; three radial spines on its margin of equal size and equidistant, angular, twice as long as the diameter of the disk, spirally twisted like the horns of Antilope strepsiceros.

Dimensions.—Diameter of the disk 0.15; length of the spines 0.3, basal breadth 0.02.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

Subgenus 2. Spongotripodium, Haeckel.

Definition.—Radial spines of different size or at different distances; triangle either isosceles or irregular.

4. Spongotripus ypsilon, n. sp.

Spongy disk triangular, isosceles, with convex sides; three spines angular, of different size and at different distances; the odd spine straight and twice as long as the two paired spines, which are more approximated and curved concavely one to the other, like .

Dimensions.—Diameter of the disk 0.12; length of the odd spine 0.2, of the paired spines 0.1, basal breadth 0.04.

Habitat.—Pacific, central area, Station 274, depth 2750 fathoms.

5. Spongotripus irregularis, n. sp.

Spongy disk circular; three spines conical, irregularly curved, all three of different size, and at irregular distances; once to three times as long as the diameter of the disk; margin of the disk thorny.

Dimensions.—Diameter of the disk 0.1; length of the spines 0.1 to 0.3, basal breadth 0.05.

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

Genus 257. Spongostaurus,^[296] Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with four solid radial spines on the margin of the circular or square disk, commonly crossed in two equatorial diameters perpendicular one to another.

The genus Staurodictya exhibits four marginal spines in cross form. Commonly the cross is regular and rectangular, the four spines being opposite in pairs in two perpendicular diameters; sometimes more or less irregular. The genus repeats Staurodictya among the Porodiscida, Staurocyclia among the Coccodiscida.

1. Spongostaurus cruciatus, n. sp.

Spongy disk circular; four radial spines on its margin opposite in two crossed equatorial diameters, perpendicular one to another, conical, about as long as the diameter of the disk.

Dimensions.—Diameter of the disk 0.16; length of the spines 0.18, basal breadth 0.04.

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

2. Spongostaurus serratus, n. sp.

Spongy disk circular; four crossed radial spines very large, twice to three times as long as the diameter of the central disk, serrated on both edges, with two rows of strong conical perpendicular teeth (similar to the saw of Pristis antiquorum).

Dimensions.—Diameter of the disk 0.1; length of the spines 0.2 to 0.3, breadth 0.02.

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

3. Spongostaurus hastatus, n. sp.

Spongy disk square, with concave sides; four crossed radial spines cylindrical, on the broader distal end spear-shaped or nearly lanceolate, one and a half times as long as the diameter of the disk.

Dimensions.—Diameter of the disk 0.13; length of the spines 0.2, basal breadth 0.01, distal breadth 0.03.

Habitat.—Tropical Atlantic, Station 347, surface.

4. Spongostaurus quadratus, n. sp.

Spongy disk square, with rectilinear sides; four crossed radial spines pyramidal, arising from the corners of the square, about as long as its half diagonal.

Dimensions.—Diameter of the disk 0.16; length of the spines 0.08, basal breadth 0.02.

Habitat.—Pacific, central area, Station 271, surface.

Genus 258. Stylotrochus,^[297] Haeckel, 1862, Monogr. d. Radiol., p. 463.

Definition.—Spongodiscida with numerous solid radial spines on the margin of the disk (five to ten or more), all situated in the equatorial plane.

The genus Stylotrochus comprises those Spongodiscida in which the margin of the circular disk bears numerous radial spines. All these spines lie in the same equatorial plane, whilst in the following genus they are disposed over the whole surface of the disk. Stylotrochus corresponds to Astrocyclia among the Coccodiscida, to Stylodictya among the Porodiscida. The spongy framework of the disk is either quite irregular (Stylotrochiscus), or includes in the middle part some concentric circular rings (Stylospongia).

Subgenus 1. Stylotrochiscus, Haeckel.

Definition.—Spongy framework of the whole disk irregular, without concentric circular rings or spiral convolutions.

1. Stylotrochus arachnius, Haeckel.

Spongotrochus arachnius, Haeckel, 1862, Monogr. d. Radiol., p. 464.

Spongy framework of the whole disk irregular. Eight to twelve marginal spines very long and thin, bristle-shaped, twice to four times as long as the diameter of the disk. (Very similar to the common Stylodictya arachnia, but without concentric circular rings and sieve-plates, with quite irregular network of fine bars.)

Dimensions.—Diameter of the disk 0.12 to 0.15; length of the radial spines 0.2 to 0.6, basal breadth 0.001.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface; also fossil in Tertiary rocks of Barbados and the Mediterranean.

2. Stylotrochus craticulatus, Haeckel.

Spongotrochus craticulatus, Stöhr, 1880, Palæontogr., vol. xxvi. p. 118, Taf. vi. fig. 12.

? Spongodiscus aculeatus, Ehrenberg, 1854, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 246.

Spongy framework of the whole disk irregular. Sixteen to twenty short marginal spines (twice to four times as long as the diameter of one mesh of the framework), free prolongations of internal radial beams which arise from the darker centre of the disk. (The interruption of the disk-margin on one point of its circumference, figured by Stöhr as osculum or "Mündungs-Oeffnung," is probably an accidental abnormality; I did not find it in other specimens.)

Dimensions.—Diameter of the disk 0.2 to 0.25; length of the radial spines 0.005 to 0.018, basal breadth 0.001 to 0.003.

Habitat.—Pacific, central area, Stations 266 to 268, surface; fossil in Barbados and Sicily.

3. Stylotrochus helianthus, n. sp.

Spongy framework of the whole disk irregular. Thirty to fifty very large, conical radial spines, about as long as the diameter of the disk, and at the base two to four times as broad as one mesh of the framework (without internal prolongations).

Dimensions.—Diameter of the disk 0.15 to 0.2; length of the radial spines 0.16 to 0.24, basal breadth 0.008 to 0.016.

Habitat.—Pacific, central area, Station 272, surface.

4. Stylotrochus rhabdostylus, Haeckel.

Spongosphæra rhabdostyla, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 256, Taf. xxvi. figs. 1, 2.

Spongy framework of the whole disk irregular. Four very large marginal primary spines crossed in two equatorial diameters, perpendicular one to another, and between them numerous (twelve to twenty or more) smaller secondary spines. The latter arise from the margin, whilst the former pierce the disk and are nearly united in its centre. All the spines are cylindrical, the smaller as broad as one mesh, the larger three to six times as broad.

Dimensions.—Diameter of the disk 0.2; length of the four main spines 0.15 to 0.3, breadth 0.01 to 0.02; length of the accessory spines 0.05 to 0.1, breadth 0.005.

Habitat.—Fossil in the rocks of Barbados.

5. Stylotrochus heteracanthus, Haeckel.

Spongotrochus heteracanthus, Haeckel, 1862, Monogr. d. Radiol., p. 464.

Spongy framework of the whole disk irregular. Ten very long needle-shaped marginal spines (symmetrically distributed), and between them numerous very fine, shorter, accessory, bristle-shaped spines.

Dimensions.—Diameter of the disk 0.16; length of the main spines 0.16, basal breadth 0.002; length of the secondary spines 0.03.

Habitat.—Mediterranean (Messina), surface.

Subgenus 2. Stylospongia, Haeckel, 1862, Monogr. d. Radiol., p. 473.

Definition.—Spongy framework of the disk in the inner part with concentric rings or spiral convolutions, in the outer part quite irregular.

6. Stylotrochus huxleyi, Haeckel.

Stylospongia huxleyi, Haeckel, 1862, Monogr. d. Radiol., p. 473, Taf. xxviii. fig. 7.

Spongy framework of the disk in the inner part with five concentric rings, in the outer part quite irregular. Ten marginal spines, conical at the base, about as long as the radius of the disk, without inner piercing prolongations.

Dimensions.—Diameter of the disk 0.12; length of the radial spines 0.06, basal breadth 0.003.

Habitat.—Mediterranean (Messina), Haeckel.

7. Stylotrochus geddesii, n. sp. (Pl. 41, fig. 11).

Stylospongidium geddesii, Haeckel, 1881, Atlas (pl. xli. fig. 11).

Spongy framework of the disk in the inner part with four to eight concentric rings (or partially spiral convolutions), in the outer part quite irregular. Thirty to fifty pyramidal marginal spines of variable size, one-fourth to one-half as long as the radius of the disk, outer prolongations of inner piercing radial beams, which arise from various concentric rings. I call this interesting species, which is intermediate between Stylodictya and Stylotrochus, in honour of the morphologist Mr. Patrick Geddes of Edinburgh.

Dimensions.—Diameter of the disk 0.15 to 0.25; length of the radial spines 0.03 to 0.06, basal breadth 0.004 to 0.01.

Habitat.—Pacific, central area, Stations 270 to 274, in 2350 to 2925 fathoms.

Genus 259. Spongotrochus,^[298] Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 844.

Definition.—Spongodiscida with numerous solid radial spines (five to ten or more), which are scattered over the whole surface and the margin of the disk, or regularly disposed on both sides of it.

The genus Spongotrochus differs from the foregoing and nearly allied genus by the distribution of the numerous radial spines. These are not confined to the margin of the disk, but also scattered on its whole surface, and sometimes symmetrically disposed on both its sides in a regular manner. Also in this genus the spongy framework is sometimes quite irregular (Spongotrochiscus), at other times in the middle part with enclosed concentric rings (Stylospongidium).

Subgenus 1. Spongotrochiscus, Haeckel, 1862, Monogr. d. Radiol., p. 463.

Definition.—Spongy framework of the whole disk irregular, without concentric rings or spiral convolutions.

1. Spongotrochus brevispinus, Haeckel.

Spongotrochus brevispinus, Haeckel, 1862, Monogr. d. Radiol., p. 462, Taf. xxvii. figs. 4, 5.

Spongy framework of the whole disk irregular, everywhere equal. The whole surface of the disk covered with numerous short, needle-shaped, radial spines, about as long as the thickness of the disk, which is one-fifth of its diameter.

Dimensions.—Diameter of the disk 0.18; length of the radial spines 0.03 to 0.04, basal breadth 0.002.

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

2. Spongotrochus multispinus, n. sp.

Spongy framework of the whole disk irregular, in the centre darker. The whole surface of the disk covered with numerous conical radial spines, about as long as the radius of the disk.

Dimensions.—Diameter of the disk 0.22; length of the radial spines 0.1, basal breadth 0.008.

Habitat.—Pacific, central area, Stations 271 to 274, surface.

3. Spongotrochus longispinus, Haeckel.

Spongotrochus longispinus, Haeckel, 1862, Monogr. d. Radiol., p. 463, Taf xxvii. figs. 2, 3.

Spongy framework of the whole disk irregular, everywhere equal. Surface thorny. Twenty long, needle-shaped, radial spines, about as long as the diameter of the disk, symmetrically distributed in pairs on both flat sides of the disk, so that the opposite pairs lie in five equidistant, meridian planes (compare the figures).

Dimensions.—Diameter of the disk 0.2; length of the twenty radial spines 0.2, basal breadth 0.001.

Habitat.—Mediterranean (Messina), surface.

Subgenus 2. Stylospongidium, Haeckel, 1881, Prodromus, p. 460.

Definition.—Spongy framework of the disk in the inner part with concentric rings or spiral convolutions, in the outer part quite irregular.

4. Spongotrochus scutella, n. sp.

Spongotrochus ehrenbergii, Bütschli, 1882, L. N. 41, Taf. xxvi. figs. 1a, 1b.

Spongy framework of the disk in the inner part with four to six concentric rings, in the outer part quite irregular. The whole surface of the disk covered with bristle-shaped radial spines, about half as long as the radius of the disk.

Dimensions.—Diameter of the disk 0.24; length of the radial spines 0.06, basal breadth 0.02.

Habitat.—Antarctic Ocean, Station 157, depth 1950 fathoms.

5. Spongotrochus parma, n. sp.

Spongy framework of the disk in the inner part with five to eight spiral convolutions (or partly concentric rings), in the outer part quite irregular. Thirty to forty long, bristle-shaped, radial spines, about as long as the diameter of the disk, disposed on both flat sides of the disk, but not on the margin.

Dimensions.—Diameter of the disk 0.16; length of the radial spines 0.18, basal breadth 0.003.

Habitat.—South Atlantic, Station 325, surface.

Subfamily 3. Spongobrachida, Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with two or more (commonly three or four) spongy radial arms on the margin of the disk, situated in its equatorial plane (with or without a connecting patagium between the arms).

Genus 260. Spongolena,^[299] n. gen.

Definition.—Spongodiscida with two opposite spongy arms on the margin of the disk, without a connecting patagium.

The genus Spongolena opens the series of the Spongobrachida, or of the Spongodiscida provided with radial spongy arms on the margin of the disk. Spongolena is the most simple form of this subfamily, and bears only two simple opposite arms, without a connecting patagium. It corresponds to Amphibrachium (Porodiscida) and to Diplactura (Coccodiscida). Also there is no patagium. Spongolena may easily be confounded with Spongurus (compare my Prodromus, 1881, p. 461); but in the true Spongurus (an ellipsoid) the transverse section is circular, in Spongolena elliptical.

1. Spongolena rhopalura, n. sp.

Arms club-shaped, three times as long as broad, at the rounded distal end twice as broad as at the base, and twice as long as the diameter of the circular central disk. Surface nearly smooth.

Dimensions.—Radius of the arms (or the distance from the centre to the distal arm-end) 0.16, distal breadth 0.05, basal breadth 0.03.

Habitat.—Pacific, central area, Station 273, depth 2350 fathoms.

2. Spongolena spongura, n. sp.

Arms nearly cylindrical, twice as long as broad, and a little longer than the diameter of the elliptical central disk. Surface thorny, some longer bristle-shaped spines on the distal end of the arms. (Very similar to the ellipsoid Spongurus cylindricus, Monogr. d. Radiol., p. 465, Taf. xxvii. fig. 1, but differs in the compressed lenticular (not ellipsoidal) form of the central disk; the transverse section of the arm is elliptical, not circular.)

Dimensions.—Radius of the arms 0.1, breadth 0.04.

Habitat.—Pacific, central area, Station 270, depth 2925 fathoms.

3. Spongolena cypselura, n. sp.

Arms nearly triangular, not longer than broad, about half as large as the elliptical central disk, at the broader distal end with two very large, widely divergent lateral spines, and between them several smaller, like the tail of a swallow. Surface thorny.

Dimensions.—Radius of the arms 0.2, distal breadth (without spines) 0.15, basal breadth 0.07.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

Genus 261. Spongobrachium,^[300] Haeckel, 1881, Prodromus, p. 461.

Definition.—Spongodiscida with two opposite spongy arms on the margin of the disk, connected by a spongy patagium of different texture.

The genus Spongobrachium differs from the foregoing only in the loose spongy patagium, which envelops both opposite spongy arms. It corresponds to Amphymenium among the Porodiscida and to Amphiactura among the Coccodiscida.

1. Spongobrachium ellipticum, Haeckel.

Spongocyclia elliptica, Haeckel, 1862, Monogr. d. Radiol., p. 470, Taf. xxviii. fig. 2.

Spongodiscus ellipticus, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 844.

Arms nearly square, scarcely as long and broad as the radius of the circular central disk, at the broader distal end truncated. Patagium complete, enveloping the whole disk with the arms, and forming a larger elliptical disk of looser framework. (In my Monograph, 1862, loc. cit., I had not distinguished the opposite darker arms, opposite in the longer axis of the elliptical disk, from the enveloping looser framework of the patagium. In larger specimens of the Challenger collection this distinction is very evident.)

Dimensions.—Radius of the arms 0.12, breadth 0.05; major axis of the elliptical patagium 0.24, minor 0.16.

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

2. Spongobrachium lanceolatum, n. sp.

Arms club-shaped, twice as long as broad, at the distal end pointed, five times as long as the radius of the circular central disk. Patagium complete, enveloping the whole disk with the arms, and forming a larger lanceolate disk of looser framework. (Similar in form to Amphymenium pupula, Pl. 44, fig. 8, but with an irregular spongy framework and pointed ends.)

Dimensions.—Radius of the arms 0.16, breadth 0.05; major axis of the lanceolate patagium 0.32, minor axis 0.12.

Habitat.—Pacific, central area, Station 270, surface.

Genus 262. Rhopalodictyum,^[301] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 830.

Definition.—Spongodiscida with three spongy arms on the margin of the circular or triangular disk, without a connecting patagium.

The genus Rhopalodictyum comprises those very common forms of Spongodiscida in which the margin of the disk is provided with three simple, free, spongy arms. It corresponds to Dictyastrum and Rhopalastrum among the Porodiscida, to Trigonactura among the Coccodiscida. The typical species of this genus is Rhopalodictyum abyssorum of Ehrenberg, the only species figured by him. His diagnosis of the genus was very insufficient, and agreed with that of his Dictyastrum (compare above the improved diagnosis of this genus, p. 526, and my Monograph, p. 466).