Genus 572. Sethoconus,^[189] Haeckel, 1881, Prodromus, p. 430.

Definition.—Sethocorida (vel Dicyrtida eradiata aperta) with conical or campanulate, gradually dilated thorax and wide open mouth. Cephalis with one or more horns.

The genus Sethoconus is the oldest and simplest form of the Sethocorida, or of those Dicyrtida in which the simple thorax bears no apophyses and has the mouth open and not closed by a basal lattice-plate. Probably all those eradiate Sethocorida have been derived either from triradiate Sethopilida (Lychnocanium), or from multiradiate Sethophormida (Sethophormis, Anthocyrtis ?) by loss of the radial ribs and feet. In Sethoconus the thorax is more or less conical, sometimes more campanulate, commonly smooth, in some species covered with spines. The cephalis is usually small, with rudimentary collar septum, at other times large, with distinct cortinar septum. Correspondingly, the genus may be divided into different groups, which here are enumerated as subgenera.

Subgenus 1. Conarachnium, Haeckel, 1881, Prodromus, p. 430. (= Ceratocyrtis, Bütschli), 1882, loc. cit., p. 536.

Definition.—Cephalis relatively large, with distinct collar septum and numerous pores. Thorax smooth.

1. Sethoconus trochus, Haeckel.

Cephalis ovate, relatively large, with a pyramidal horn of the same length, and three pairs of large opposite pores, on each side of a vertical septum. Thorax wide, conical, about as long as broad, with nearly straight outlines; its pores regular, circular, hexagonally framed, of the same size as the cephalic pores.

Dimensions.—Cephalis 0.03 long, 0.02 broad; thorax 0.06 long, 0.06 broad.

Habitat.—Tropical Pacific, Stations 200 to 281, surface.

2. Sethoconus cucullaris, Haeckel.

Cephalis subspherical, thorny, relatively large, with a conical horn of the same length, and small circular pores. Thorax wide, conical, enveloping the lower hidden half of the cephalis, about as long as broad, with slightly convex outlines; its pores subregular, circular, half as broad as the cephalis.

Dimensions.—Cephalis 0.03 long, 0.02 broad; thorax 0.15 long, 0.14 broad.

Habitat.—Fossil in Barbados.

3. Sethoconus pileus, n. sp.

Cephalis subspherical, free, with distinct collar stricture, a conical oblique horn of the same length, and small, irregular, roundish pores. Thorax flatly conical, about half as long as broad, with straight outlines; its pores subregular, hexagonal, half as broad as the cephalis, with very thin bars.

Dimensions.—Cephalis 0.02 long, 0.02 broad; thorax 0.08 long, 0.16 broad.

Habitat.—Central Pacific, Stations 262 to 274, surface.

4. Sethoconus ampliatus, Haeckel.

Cephalis, hemispherical, thorny, with a conical horn of twice the length; it is separated from the thorax by a complete internal collar septum, but without external collar stricture. Thorax flatly conical, about half as long as broad, with straight outlines; its pores subregular, hexagonal, about as large as the cephalis, with thin bars.

Dimensions.—Cephalis 0.015 long, 0.03 broad; thorax 0.08 long, 0.18 broad.

Habitat.—Fossil in Barbados.

5. Sethoconus mitra, Haeckel.

Cephalis ovate, with slight collar stricture (not distinct enough in Ehrenberg's figure), with few large pores, and a conical stout horn of the same length. Thorax campanulate, conical, twice as long as broad, with slightly convex outlines; its pores subregular, roundish, increasing in size towards the mouth, the largest as broad as the cephalis.

Dimensions.—Cephalis 0.03 long, 0.02 broad; thorax 0.12 long, 0.07 broad.

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

6. Sethoconus rayianus, n. sp. (Pl. 58, fig. 6).

Cephalis ovate, with obliterated collar stricture (but distinct internal septum), with small, irregular pores, and two to four divergent horns, which are longer than the cephalis, and two or three of which are forked. Thorax tent-shaped, conical, two-thirds as long as broad, with slightly concave outlines, and subregular, hexagonal pores, gradually increasing towards the mouth, the largest half as broad as the cephalis. This elegant species is dedicated to Dr. Ray, the discoverer of many rare Radiolarians in the Challenger collection.

Dimensions.—Cephalis 0.03 long, 0.02 broad; thorax 0.08 long, 0.12 broad.

Habitat.—Central Pacific, Stations 266 to 272, surface.

7. Sethoconus cervus, Haeckel.

Cephalis subspherical, with slight collar stricture, small circular pores, and two to four divergent horns, one or two of which are forked. Thorax wide, conical, about as long as broad, with straight outlines and irregular, polygonal pores, gradually increasing towards the mouth; the largest as broad as the cephalis.

Dimensions.—Cephalis 0.015 long, 0.02 broad; thorax 0.08 long, 0.08 broad.

Habitat.—Indian Ocean; Maldive Islands, surface (Haeckel); Zanzibar, depth 2200 fathoms (Pullen).

8. Sethoconus lophophæna, n. sp.

Cephalis subspherical, with distinct collar stricture, small circular pores, and numerous (twelve to sixteen) radial, bristle-shaped horns of different lengths. Thorax wide, conical, somewhat longer than broad, with slightly convex outlines, and subregular, hexagonal pores, increasing gradually in size towards the mouth; the largest twice as broad as the cephalis.

Dimensions.—Cephalis 0.03 long, 0.04 broad; thorax 0.2 long, 0.16 broad.

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

9. Sethoconus larvatus, Haeckel.

Cephalis subspherical, large, with sharp collar stricture, and numerous (five to ten or more) radial, conical (partly forked) horns of different lengths. Thorax wide, conical, somewhat broader than long, with straight outlines. Pores of both joints very irregular, roundish, of very different sizes and form.

Dimensions.—Cephalis 0.04 long, 0.05 broad; thorax 0.1 long, 0.12 broad.

Habitat.—Fossil in Barbados.

10. Sethoconus nassa, Haeckel.

Cephalis slenderly ovate, with sharp collar stricture, few scattered pores, and a very stout, pyramidal horn of the same length, which is surrounded at the base by three short, divergent, ascending spines (perhaps the remnants of the three cortinar rods of Eucecryphalus, &c. ?). Thorax slender, conical, with straight outlines, and small, dense, regular, circular pores of equal size.

Dimensions.—Cephalis 0.04 long, 0.02 broad; thorax 0.12 long, 0.08 broad.

Habitat.—Fossil in Barbados.

11. Sethoconus tabulatus, Haeckel.

Cephalis subspherical, with slight collar stricture, and numerous small, irregular pores, without horn, or with a small conical horn. Thorax slenderly conical, with straight outlines, and large, regular, hexagonal pores. Mouth truncate. (In the specimen I examined the thorax was longer and more conically dilated; the cephalis had a distinct small horn.)

Dimensions.—Cephalis 0.02 long, 0.03 broad; thorax 0.08 long, 0.06 broad.

Habitat.—North Atlantic, Antilles, depth 1600 fathoms (Ehrenberg); Station 347, depth 2250 fathoms.

Subgenus 2. Cornutellium (vel Ceratarachnium), Haeckel, 1881, Prodromus, p. 430.

Definition.—Cephalis very small, rudimentary, hyaline, without distinct collar septum, and without pores (or with scarce, rudimentary pores). Thorax smooth.

12. Sethoconus hexagonalis, Haeckel.

Cephalis very small, subspherical, hyaline, without pores, with a rudimentary horn of half the length. Thorax slenderly conical, or bottle-shaped, twice to three times as long as broad; in the lower half nearly cylindrical, with very thin, thread-like bars, and regular, hexagonal pores, increasing in size towards the mouth.

Dimensions.—Cephalis 0.005 diameter, thorax 0.12 long, 0.05 broad.

Habitat.—Indian Ocean, Zanzibar, depth 2200 fathoms (Pullen).

13. Sethoconus verrucosus, Haeckel.

Cephalis very small, subspherical, hyaline, without pores, with a rudimentary horn of half the length. Thorax slenderly conical, or bottle-shaped, with little convex outlines; three to four times as long as broad, papillate, with regular, circular pores, which are included by rhombic frames, and increase in size towards the mouth.

Dimensions.—Cephalis 0.004 diameter, thorax 0.12 long, 0.035 broad.

Habitat.—Indian Ocean (Zanzibar), depth 2200 fathoms (Pullen).

14. Sethoconus orthoceras, n. sp. (Pl. 54, fig. 11).

Cephalis very small, conical, hyaline, without pores, with a double internal stricture, and a very short, rudimentary horn. Thorax slenderly conical, with undulate outlines, three to four times as long as broad, with subregular, roundish pores, gradually increasing in size towards the mouth.

Dimensions.—Cephalis 0.02 long, 0.01 broad; thorax 0.16 long, 0.04 to 0.08 broad.

Habitat.—South Atlantic, Station 325, surface.

15. Sethoconus profundus, Haeckel.

Cephalis very small, spherical, hyaline without pores and internal stricture, with a very short, rudimentary horn. Thorax slenderly conical with straight outlines, three to four times as long as broad, with subregular, circular pores, gradually increasing in size towards the mouth.

Dimensions.—Cephalis 0.004 to 0.008 diameter, thorax 0.08 to 0.12 long, 0.03 to 0.04 broad.

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

16. Sethoconus trichostylus, Haeckel.

Cephalis very small, conical, hyaline, without pores, with a very long, bristle-shaped, spirally twisted horn, longer than the whole shell. Thorax slenderly conical, with straight outlines, and very small, regular, circular pores of nearly equal size, which are separated by broader bars and spirally ascending oblique crests (according to the figure).

Dimensions.—Cephalis 0.004 long, 0.002 broad; thorax 0.06 long, 0.04 broad.

Habitat.—North Pacific (California), depth 2600 fathoms.

17. Sethoconus longisetus, Haeckel.

Cephalis very small, spherical, hyaline, without pores, with a very long, bristle-shaped horn, nearly as long as the shell. Thorax slenderly conical, rough, with straight outlines, and irregular, roundish pores, gradually increasing in size towards the mouth.

Dimensions.—Cephalis 0.01 diameter, thorax 0.09 long, 0.03 broad.

Habitat.—Indian Ocean (Zanzibar), depth 2200 fathoms (Pullen).

18. Sethoconus gracilis, Haeckel.

Cephalis small, subspherical, with few scarce pores, and a stout, pyramidal horn, of the same length. Thorax slenderly conical, three to four times as long as broad, with straight outlines, and very small and numerous circular pores of equal size.

Dimensions.—Cephalis 0.015 diameter, thorax 0.12 long, 0.04 broad.

Habitat.—Fossil in Barbados.

19. Sethoconus bimarginatus, n. sp. (Pl. 54, fig. 12).

Cephalis very small, subspherical, hyaline, without pores, with a rudimentary, conical horn of the same length. Thorax slenderly conical, three times as long as broad, with undulated, little convex outlines, and irregular, roundish, double-contoured pores, arranged in nine longitudinal series, markedly increasing in size towards the mouth.

Dimensions.—Cephalis 0.01 diameter, thorax 0.16 long, 0.05 broad.

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

20. Sethoconus clathratus, Haeckel.

Cephalis very small, subspherical, hyaline, without pores, with a rudimentary horn of half the length. Thorax slenderly conical, three to four times as long as broad, smooth, with curved axis and small, regular, circular pores, nearly equal in size. This common species differs from all others of the genus by the curvation of the axis of the shell, which is more or less crescentic, or curved like a cowherd's horn; it may, therefore, represent a peculiar genus, Sethodrepanum.

Dimensions.—Cephalis 0.003 to 0.006 diameter, thorax 0.08 to 0.16 long, 0.03 to 0.05 broad.

Habitat.—Cosmopolitan; Atlantic, Pacific, many stations; fossil in Barbados and Sicily.

Subgenus 3. Phlebarachnium, Haeckel (et Cladarachnium, Haeckel), 1881,

Definition.—Cephalis small, with very small pores, and internal collar septum. Thorax spiny or thorny.

21. Sethoconus facetus, n. sp. (Pl. 55, fig. 1).

Cephalis small, hemispherical, with distinct collar septum, the same network as the thorax, and numerous bristle-shaped horns of the same length. Thorax wide, conical, about as long as broad, with slightly convex outlines; its network extremity delicate, with very small and numerous, regular, hexagonal pores, disposed in numerous divergent, longitudinal series, which are convoluted somewhat spirally around the shell axis. Surface covered with thin, scattered, bristle-shaped spines, about as long as the cephalis.

Dimensions.—Cephalis 0.02 diameter, thorax 0.2 long, 0.22 broad.

Habitat.—Central Pacific, Stations 271 to 274, surface.

22. Sethoconus anthocyrtis, n. sp. (Pl. 62, fig. 21).

Cephalis small, subspherical, with very small pores and numerous radial, bristle-shaped spines of the same length. Thorax wide, conical, about as long as broad, with parabolic outlines, its network very delicate, with subregular, hexagonal meshes. Surface with scarce, bristle-shaped spines (not represented in the figure). Mouth with a corona of numerous small, vertical spines.

Dimensions.—Cephalis 0.025 diameter, thorax 0.26 long, 0.24 broad.

Habitat.—North Pacific, Station 248, surface.

23. Sethoconus virgultus, n. sp.

Cephalis and thorax nearly of the same form and stricture as in Sethoconus facetus, but larger and wider, with the same delicate, hexagonal network (Pl. 55, fig. 1); it differs from the latter by the wider, more convex and campanulate form, but mainly by the armature of the surface, which is densely covered with thin, arborescent, bristle-shaped spines, irregularly branched, and four to eight times as large as the cephalis.

Dimensions.—Cephalis 0.02 diameter, thorax 0.32 long, 0.4 broad.

Habitat.—South Pacific, Station 288, surface.

24. Sethoconus setosus, n. sp.

Cephalis small, subspherical, with distinct collar septum, and the same network as the thorax, with numerous bristle-shaped horns of the same length. Thorax slenderly conical, twice as long as broad, with irregular, polygonal pores of little different sizes, and very thin bars. Surface covered with perpendicular, simple, bristle-shaped spines, about as long as the cephalis.

Dimensions.—Cephalis 0.02 diameter, thorax 0.12 long, 0.22 broad.

Habitat.—Central Pacific, Stations 266 to 272, surface.

25. Sethoconus venosus, n. sp. (Pl. 55, fig. 2).

Cephalis subspherical, with a stout prismatic horn twice the length, bearing three denticulate edges. The uppermost part of the thorax is supported by three diverging, radial beams arising from the deep collar stricture. Thorax wide, conical, nearly twice as long as broad, with slightly convex, thorny outlines; its delicate network is composed of very irregular, polygonal meshes of different sizes, separated by stronger bars, and of numerous very small polygonal pores separated by very thin bars inside the former. The central capsule of the figured specimen exhibited in the upper third of the thorax four large club-shaped lobes, which arose from a very small sphere enclosed in the cephalis and containing the nucleus.

Dimensions.—Cephalis 0.02 long, 0.03 broad; thorax 0.4 long, 0.3 broad.

Habitat.—Central Pacific, Station 271, surface.

Genus 573. Periarachnium,^[190] Haeckel, 1881, Prodromus, p. 430.

Definition.—Sethocorida (vel Dicyrtida eradiata aperta) with conical or campanulate, gradually dilated thorax, and widely open mouth. Primary lattice-shell enveloped by an external arachnoidal mantle. Cephalis with one or more horns.

The genus Periarachnium has been derived from those forms of the preceding Sethoconus, in which the conical thorax is covered with simple spines (Phlebarachnium) or branched spines (Cladarachnium). By communication of the branches of these spines a second outer shell is formed, which, like an arachnoidal mantle, envelops the inner primary shell.

1. Periarachnium periplectum, n. sp. (Pl. 55, fig. 11).

Cephalis hemispherical, separated from the thorax by a sharp collar stricture, from which arise three internal, diverging beams supporting its upper third. Thorax campanulate, conical, about as long as broad, with slightly convex outlines. The delicate lattice-work of the entire shell is double; the inner composed of subregular, hexagonal meshes; the outer of larger, irregular, polygonal meshes. The bars of the inner are much thicker than the thin threads of the outer. Both shells are connected by numerous bristle-shaped beams. The central capsule of the figured specimen exhibited in the upper part of the thorax three club-shaped lobes, which arose from a sphere enclosed in the cephalis and containing the nucleus.

Dimensions.—Cephalis 0.02 long, 0.03 broad; thorax 0.15 long, 0.12 broad.

Habitat.—Central Pacific, Station 271, surface.

Genus 574. Sethocephalus,^[191] Haeckel, 1881, Prodromus, p. 430.

Definition.—Sethocorida (vel Dicyrtida eradiata aperta) with discoidal, flatly expanded thorax. Cephalis large, without horn.

The genus Sethocephalus (formerly proposed under the name Platycryphalus) contains some few and rare Sethocorida, distinguished by the very large cephalis, the collar opening of which is wide open, not closed by cortinar beams, and surrounded by a very flat, nearly discoidal thorax, like the brim of a hat. It is possible that this peculiar genus has been derived from a Tricyrtid (Theocalyptra?) by loss of the original cephalis, and that the apparent large cephalis is the original thorax.

1. Sethocephalus eucecryphalus, n. sp. (Pl. 56, fig. 13).

Cephalis very large, campanulate-conical, with irregular, polygonal pores and thin bars. Thorax short, scarcely broader than the cephalis, beyond the sharp collar stricture expanded like the brim of a hat, with few rows of irregular, polygonal pores. (In the specimen figured the thorax was only half as broad as in another specimen found afterwards.)

Dimensions.—Cephalis 0.12 long, 0.09 broad; thorax 0.02 long, 0.12 broad.

Habitat.—South Pacific, Station 285, surface.

2. Sethocephalus platycryphalus, n. sp.

Cephalis large, hemispherical, with irregular square pores and thin bars. Thorax flatly conical, three to four times as broad as the cephalis, beyond the collar stricture expanded nearly discoidally, with a delicate network of small, subregular, hexagonal pores. (Similar in general form to Sethophormis aurelia, Pl. 55, fig. 3, but without any trace of collar beams or radial ribs.)

Dimensions.—Cephalis 0.04 long, 0.08 broad; thorax 0.04 long, 0.3 broad.

Habitat.—South Pacific, Station 289, surface.

Genus 575. Sethocyrtis,^[192] n. gen.

Definition.—Sethocorida (vel Dicyrtida eradiata aperta) with ovate or subcylindrical thorax, the mouth of which is constricted, simple, without prominent hyaline peristome. Cephalis with an apical horn.

The genus Sethocyrtis and the three following nearly allied genera differ from the three preceding genera of Sethocorida in the form of the thorax, which is not gradually dilated, conical, but cylindrical or ovate, with more or less constricted mouth. Sethocyrtis may be derived from Anthocyrtis by loss of the terminal feet. Its mouth is quite simple, without tubular or annular peristome.

1. Sethocyrtis oxycephalis, n. sp. (Pl. 62, fig. 9).

Shell rough, subconical, with slight collar stricture. Length of the two joints = 4 : 9, breadth = 3 : 8. Cephalis ovate, with a pyramidal horn of half the length. Thorax campanulate, with regular, circular pores, twice as broad as those of the cephalis. Mouth constricted, scarcely half as broad as the thorax.

Dimensions.—Cephalis 0.04 long, 0.03 broad; thorax 0.09 long, 0.08 broad.

Habitat.—Central Pacific, Stations 263 to 274, depth 2350 to 3000 fathoms.

2. Sethocyrtis cancrina, Haeckel.

Shell smooth, bottle-shaped, with obliterated collar stricture. Length of the two joints = 4 : 9, breadth = 2 : 7. Cephalis subcylindrical, with a stout conical horn of the same length, and sometimes a smaller accessory horn at its base. Thorax ovate, truncate, with regular, circular, quincuncial pores, twice as broad as those of the cephalis. Mouth little constricted, flat, nearly as broad as the thorax.

Dimensions.—Cephalis 0.04 long, 0.02 broad; thorax 0.09 long, 0.07 broad.

Habitat.—Fossil in Barbados.

3. Sethocyrtis diomedis, n. sp.

Shell thorny, pear-shaped, with slight collar stricture. Length of the two joints = 3 : 16, breadth = 4 : 20. Cephalis hemispherical, with a conical horn of twice the length. Thorax inflate, ovate, truncate at both poles, with regular, circular pores, twice as broad as those of the thorax. Mouth constricted, flat, half as broad as the thorax.

Dimensions.—Cephalis 0.03 long, 0.04 broad; thorax 0.12 to 0.16 long, 0.16 to 0.2 broad.

Habitat.—Central Pacific, Stations 265 to 268, depth 2700 to 2900 fathoms; also fossil in Barbados.

4. Sethocyrtis menelai, n. sp.

Shell spiny, pear-shaped, with sharp collar stricture. Length of the two joints = 3 : 15, breadth = 4 : 18. Cephalis subspherical, with a large, cylindro-conical horn, about as long as the whole shell. Thorax inflate, subspherical, truncate, with large, irregular, roundish pores, four to six times as large as those of the cephalis. Mouth constricted, flat, one-third as broad as the thorax.

Dimensions.—Cephalis 0.03 long, 0.04 broad; thorax 0.15 long, 0.18 broad.

Habitat.—Fossil in Barbados.

5. Sethocyrtis subacuta, Haeckel.

Shell smooth, pear-shaped, with sharp collar stricture. Length of the two joints = 1 : 4, breadth = 1 : 3. Cephalis subspherical, with small, irregular pores and a rudimentary horn of half the length. Thorax ovate, with large, subregular, hexagonal pores and thin bars between them. Mouth constricted, flat, half as broad as the thorax, without prominent peristome.

Dimensions.—Cephalis 0.02 long, 0.02 broad; thorax 0.08 long, 0.06 broad.

Habitat.—Philippine Sea, depth 3300 fathoms (Ehrenberg).

6. Sethocyrtis pleuracantha, Haeckel.

Shell smooth, bottle-shaped, with distinct collar stricture. Length of the two joints = 2 : 4, breadth = 1 : 3. Cephalis slenderly ovate, with an excentric pyramidal horn of the same length. Thorax inflate, ovate, with irregular, roundish pores and thin bars between them. Mouth constricted, flat, half as broad as the thorax, without prominent peristome.

Dimensions.—Cephalis 0.04 long, 0.02 broad; thorax 0.08 long, 0.06 broad.

Habitat.—Tropical Pacific, Stations 200, 225, 266, 274, &c., at various depths.

7. Sethocyrtis agamemnonis, n. sp. (Pl. 62, figs. 11, a, b).

Shell pear-shaped, rough, with sharp collar stricture. Length of the two joints = 2 : 10, breadth = 3 : 8. Cephalis subspherical, with very small pores and a small, pyramidal horn of half the length. Thorax inflate, ovate; in the uppermost part (beyond the collar stricture) with a ring of six to nine very large roundish pores, which are twice to four times as broad as the other irregular, roundish pores. (The shell is seen in fig. 11 from the apical pole, in fig. 11a with the cephalis, in fig. 11b without it, exhibiting the four central collar pores of the cortinar septum.) Mouth truncate, without prominent peristome.

Dimensions.—Cephalis 0.02 long, 0.03 broad; thorax 0.1 long, 0.08 broad.

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

8. Sethocyrtis cassis, Haeckel.

Shell pear-shaped, smooth, with obliterated collar stricture. Length of the two joints = 4 : 13, breadth = 3 : 12. Cephalis ovate, with a conical horn of half the length. Thorax inflate, ovate, with subregular, circular, quincuncial pores, twice to three times as broad as the bars. Mouth constricted, truncate, two-thirds as broad as the thorax, without prominent peristome.

Dimensions.—Cephalis 0.04 long, 0.03 broad; thorax 0.13 long, 0.12 broad.

Habitat.—Fossil in Tertiary rocks of Sicily (Caltanisetta).

Genus 576. Sethocorys,^[193] Haeckel, 1881, Prodromus, p. 430.

Definition.—Sethocorida (vel Dicyrtida eradiata aperta) with ovate or sub-cylindrical thorax, the mouth of which is constricted and prolonged into a ring-like peristome. Cephalis with an apical horn.

The genus Sethocorys differs from the preceding Sethocyrtis, its ancestral form, in the form of the constricted mouth, which is prolonged into a prominent, hyaline, tubular, or annular peristome.

1. Sethocorys achillis, n. sp. (Pl. 62, fig. 8).

Shell rough, pear-shaped, with distinct collar stricture. Length of the two joints = 4 : 8, breadth = 3 : 8. Cephalis ovate, with a stout pyramidal horn of half the length. Thorax nearly spherical, with regular, circular, quincuncial pores of the same breadth as the cephalic pores. Mouth constricted, half as broad as the thorax, with a broad, smooth, striated peristome.

Dimensions.—Cephalis 0.04 long, 0.03 broad; thorax 0.08 long, 0.08 broad.

Habitat.—Cosmopolitan; Mediterranean (Corfu), Atlantic, Indian, Pacific; many stations, at various depths.

2. Sethocorys patrocli, n. sp.

Shell thorny, pear-shaped, with slight collar stricture. Length of the two joints = 4 : 12, breadth = 3 : 10. Cephalis ovate, with a pyramidal horn of twice the length. Thorax ovate, truncate at both poles, with regular, circular pores, twice as broad as the cephalic pores. Mouth constricted, half as broad as the thorax, with a broad, smooth, prominent peristome.

Dimensions.—Cephalis 0.04 long, 0.03 broad; thorax 0.12 long, 0.1 broad.

Habitat.—Central Pacific, Stations 263 to 274, depth 2350 to 3000 fathoms.

3. Sethocorys armadillo, Haeckel.

Shell slenderly ovate, smooth, with deep collar stricture. Length of the two joints = 3 : 10, breadth = 4 : 6. Cephalis ovate, at the apex thorny, with a conical horn of the same length. Thorax smooth, ovate, truncate, with small, regular, circular pores, disposed in from twelve to fifteen transverse rows of the same breadth as the cephalic pores. Mouth constricted, half as broad as the thorax, with a broad, hyaline, prominent peristome.

Dimensions.—Cephalis 0.03 long, 0.04 broad; thorax 0.1 long, 0.06 broad.

Habitat.—Fossil in Barbados.

4. Sethocorys odysseus, n. sp. (Pl. 62, fig. 10).

Shell ovate, smooth, with obliterated collar stricture. Length of the two joints = 2 : 9, breadth = 4 : 8. Cephalis hemispherical, with a slender, conical horn of the same length. Thorax nearly spherical, with regular, circular pores, of the same breadth as the cephalic pores, quincuncially disposed. Mouth constricted, only one-third as broad as the thorax, with a broad, hyaline, prominent peristome.

Dimensions.—Cephalis 0.02 long, 0.04 broad; thorax 0.09 long, 0.08 broad.

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

5. Sethocorys amphora, Haeckel.

Shell ovate, mouth with distinct collar stricture. Length of the two joints = 1 : 5, breadth = 2 : 4. Cephalis hemispherical, with a short conical horn of half the length. Thorax ovate, truncate, with small, regular, circular, quincuncial pores. Mouth constricted, half as broad as the thorax, with a narrow, prominent, hyaline peristome.

Dimensions.—Cephalis 0.015 long, 0.03 broad; thorax 0.07 long, 0.06 broad.

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

6. Sethocorys ajacis, n. sp.

Shell slenderly ovate, smooth, without external collar stricture, but with an internal septum. Length of the two joints = 1 : 3, breadth = 1 : 2. Cephalis conical, with a large pyramidal horn of twice the length, and sometimes with a smaller accessory horn at its base; its pores scarce, irregular. Thorax ovate, truncate, hyaline, in the greater part without pores, in the smaller part with from two to four transverse rows of small, circular pores only. Mouth constricted, with a large cylindrical, tubular, hyaline peristome, half as long as the shell.

Dimensions.—Cephalis 0.03 long, 0.04 broad; thorax 0.09 long, 0.07 broad.

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

Genus 577. Lophophæna,^[194] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

Definition.—Sethocorida (vel Dicyrtida eradiata aperta) with ovate or subcylindrical thorax, the mouth of which is either truncate or constricted. Cephalis armed with several large horns.

The genus Lophophæna differs from the nearly allied Sethocorys and Dictyocephalus only in the armature of the large cephalis, which bears a group of large horns, often arranged in a corona of radial spines. Sometimes these spines are connected by anastomosing branches (like Arachnocorys).

Subgenus 1. Lophophænula, Haeckel.

Definition.—Horns of the cephalis simple, free, radial spines, neither branched nor connected.

1. Lophophæna galea, Ehrenberg.

Shell with slight collar stricture. Length of the two joints = 5 : 4, breadth = 5 : 6. Cephalis subglobular, with numerous bristle-shaped, radial spines, about as long as its radius. Thorax about the same size, truncate, conical, smooth, with wide open mouth. Pores in both joints of equal size, small, regular, circular.

Dimensions.—Cephalis 0.05 long, 0.05 broad; thorax 0.04 long, 0.06 broad.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms; also fossil in Barbados.

3. Lophophæna radians, Ehrenberg.