Definition.—Theopilida (vel Tricyrtida triradiata aperta) with three simple, free lateral wings arising from the sides of the thorax.
The genus Pterocorys, comprising numerous and some very common species, may be one of the oldest and most primitive Theopilida, and is perhaps the common ancestral form of all Tricyrtida. It exhibits three free lateral wings, arising from the sides of the thorax, like Lithomelissa among the Dicyrtida, and may be derived directly from this genus by development of an abdomen. The latter is commonly cylindrical or ovate, with a wide open mouth, whilst the thorax is either campanulate or three-sided and pyramidal.
Definition.—Horn of the cephalis simple. Abdomen not prolonged into a narrow tube.
1. Pterocorys campanula, n. sp. (Pl. 71, fig. 3).
Shell campanulate, with two distinct strictures. Length of the three joints = 2 : 3 : 2, breadth = 2 : 4 : 6. Cephalis subovate, with a pyramidal horn of the same length. Thorax subconical, in the middle zone with three conical, horizontal wings, shorter than the cephalis, from which three thin ribs are decurrent to the mouth. Abdomen short and much dilated, with wide, truncate mouth. Pores nearly equal, small, subregular, circular.
Dimensions.—Length of the three joints, a 0.04, b 0.06, c 0.04; breadth, a 0.03, b 0.08, c 0.12.
Habitat.—Central Pacific, Stations 266 to 274, surface.
2. Pterocorys carinata, Haeckel.
Eucyrtidium carinatum, Haeckel, 1862, Monogr. d. Radiol., p. 322, Taf. vii. figs. 4-7.
Shell subovate, with two distinct strictures. Length of the three joints = 1 : 2 : 3, breadth = 1 : 3 : 4. Cephalis ovate, with a pyramidal horn of twice the length. Thorax campanulate, with three decurrent crests, from which in the lower part three small conical wings arise, shorter than the cephalis. Abdomen barrel-shaped, inflated, with wide, truncate mouth. Pores everywhere equal, small, regular, circular, quincuncial.
Dimensions.—Length of the three joints, a 0.25, b 0.05, c 0.075; breadth, a 0.25, b 0.09, c 0.1.
Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific; many stations, surface.
3. Pterocorys sabæ, Haeckel.
Pterocanium sabæ, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 299, Taf. x. fig. 17.
Shell campanulate or subconical, with two sharp strictures. Length of the three joints = 1 : 3 : 4, breadth = 1 : 4 : 5. Cephalis subspherical, with a conical horn of the same length. Thorax subconical, in the lower third with three small, conical, little curved wings, shorter than the cephalis. Abdomen dilated towards the wide, truncate mouth. Pores subregular, circular, gradually increasing in size from the collar towards the mouth.
Dimensions.—Length of the three joints, a 0.025, b 0.06, c 0.08; breadth, a 0.02, b 0.08, c 0.09.
Habitat.—Indian Ocean, Zanzibar, 2200 fathoms (Pullen).
4. Pterocorys columba, n. sp. (Pl. 71, fig. 2).
Shell subovate, with two deep strictures. Length of the three joints = 2 : 5 : 4, breadth = 3 : 7 : 7. Cephalis hemispherical, with a curved conical horn of the same length. Thorax inflate, in the middle zone with three pyramidal downwardly divergent wings of nearly the same length. Abdomen short, inflate, little constricted towards the wide, truncate mouth. Pores all nearly equal, subregular, circular.
Dimensions.—Length of the three joints, a 0.02, b 0.05, c 0.04; breadth, a 0.03, b 0.07, c 0.07.
Habitat.—North Pacific, Station 237, surface.
5. Pterocorys falcifera, Haeckel.
Pterocanium falciferum, Stöhr, 1880, Palæontogr., vol. xxvi. p. 107, Taf. iv. fig. 15.
? Pterocanium bibrachiatum, Stöhr, 1880, Palæontogr., vol xxvi. p. 106, Taf. iv. fig. 14.
Shell subovate, with two distinct strictures. Length of the three joints = 2 : 6 : 5, breadth = 3 : 9 : 10. Cephalis subspherical, with a conical horn of the same length. Thorax hemispherical, thick-walled, rough, with three stout triangular wings, which are about as long as the shell, and curved downwards, with upper convexity. Abdomen ovate, cylindrical, with wide, truncate mouth. Pores irregular, roundish, large and small intermingled; at the base of the abdomen (below the lumbar girdle) a circle of somewhat oblong, quadrangular pores.
Dimensions.—Length of the three joints, a 0.02, b 0.06, c 0.05; breadth, a 0.03, b 0.09, c 0.1.
Habitat.—Fossil in Tertiary rocks of Sicily, Grotte (Stöhr); Caltanisetta (Haeckel).
6. Pterocorys aquila, n. sp. (Pl. 71, fig. 5).
Shell ovate, with two deep strictures. Length of the three joints = 1 : 4 : 4, breadth = 1 : 8 : 6. Cephalis hemispherical, with a slender curved horn of three times the length. Thorax hemispherical, campanulate, spiny, prolonged above the lumbar girdle into three stout, three-sided prismatic wings, which are longer than the shell, fenestrated at the base, and S-shaped, curved. Abdomen barrel-shaped, with wide, truncate mouth. Pores irregular, roundish, of very different sizes.
Dimensions.—Length of the three joints, a 0.02, b 0.08, c 0.08; breadth, a 0.03, b 0.16, c 0.12.
Habitat.—Central Pacific, Station 271, depth 2425 fathoms.
7. Pterocorys hirundo, n. sp. (Pl. 71, fig. 4).
Shell slender, ovate, with two deep strictures. Length of the three joints = 1 : 4 : 4, breadth = 2 : 5 : 5. Cephalis hemispherical, with a large pyramidal horn longer than the half shell. Thorax conical, spiny, prolonged above the lumbar girdle into three slender, triangular, prismatic wings, which are about as long as the shell, and slightly curved downwards, with lower convexity. Abdomen inflated, with wide, truncate mouth. Pores irregular, roundish, of very different sizes.
Dimensions.—Length of the three joints, a 0.03, b 0.08, c 0.08; breadth, a 0.04, b 0.1, c 0.1.
Habitat.—Central Pacific, Station 272, depth 2600 fathoms.
8. Pterocorys barbadensis, Haeckel.
Pterocanium barbadense, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 82, Taf. xvii. fig. 6.
Pterocyrtidium barbadense, Bütschli, 1882, Zeitschr. f. wiss. Zool., Bd. xxxvi., Taf. xxxiii. fig. 29, a, b.
Shell slender, smooth, with two slight strictures. Length of the three joints = 1 : 3 : 4, breadth = 2 : 4 : 4. Cephalis hemispherical, with a stout pyramidal horn of twice the length. Thorax campanulate-conical, in the lower half with three divergent, angular wings, which are slightly curved downwards, and as long as the thorax. Abdomen cylindrical, with wide, truncate mouth. Pores small, subregular, circular.
Dimensions.—Length of the three joints, a 0.02, b 0.05, c 0.07; breadth, a 0.04, b 0.07, c 0.07.
Habitat.—Fossil in Barbados.
9. Pterocorys apis, Haeckel.
Pterocodon apis, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 82, Taf. xix. fig. 3.
Shell slender, smooth, with two distinct strictures. Length of the three joints = 1 : 2 : 6, breadth = 2 : 3 : 4. Cephalis hemispherical, with a curved, conical horn of three times the length. Thorax very small, with three nearly horizontal, conical wings, which are slightly curved downwards, and twice as long as the thorax. Abdomen cylindrical, three times as long as the thorax, with wide, truncate mouth. Pores small, subregular, circular. Differs from all other species in the very small size of the thorax; the abdomen is broken off in Ehrenberg's figure.
Dimensions.—Length of the three joints, a 0.15, b 0.02, c 0.06; breadth, a 0.02, b 0.03, c 0.04.
Habitat.—Cosmopolitan; Atlantic, Pacific, many stations; also fossil in Barbados.
10. Pterocorys melitta, Haeckel.
Rhopalocanium ornatum, Bury, 1862, Polycystins of Barbados, Taf. vi. fig. 4.
Shell slender, smooth, with two deep strictures. Length of the three joints = 1 : 1 : 3, breadth = 1 : 2 : 2. Cephalis subspherical, with a pyramidal horn of twice the length. Thorax broad and short, loaf-shaped, with three conical wings, which are horizontally expanded, and half as long as the shell. Abdomen cylindrical, with wide, truncate mouth. Pores small, subregular, circular.
Dimensions.—Length of the three joints, a 0.025, b 0.03, c 0.09; breadth, a 0.03, b 0.06, c 0.06.
Habitat.—Fossil in Barbados.
11. Pterocorys turgida, Haeckel.
Lychnocanium turgidum, Ehrenberg, 1885, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 80, Taf. vii. fig. 6.
Shell thick-walled, pear-shaped, smooth, with sharp collar stricture. The lumbar stricture is not distinct externally, but is represented by a broad, internal, annular septum. Length of the three joints = 1 : 6 : 3, breadth = 2 : 7 : 6. Cephalis hemispherical, with a stout pyramidal horn of the same length. Thorax and abdomen together pear-shaped, inflated. Immediately above the lumbar stricture three stout, conical, lateral wings, as long as the cephalis, arise. Mouth very small, about as broad as the cephalis.
Dimensions.—Length of the three joints, a 0.02, b 0.12, c 0.06; breadth, a 0.03, b 0.13, c 0.12.
Habitat.—Fossil in Barbados.
Definition.—Horn of the cephalis simple. Abdomen prolonged into a narrow cylindrical tube.
12. Pterocorys tubulosa, n. sp. (Pl. 68, fig. 6).
Pterosyringium tubulosum, Haeckel, 1879, Atlas, loc. cit.
Shell thick-walled, rough, with two slight strictures. Length of the three joints = 1 : 4 : 4, breadth = 1 : 3 : 1. Cephalis hemispherical, with a conical horn of the same length. Thorax ovate, in the upper half with three ribs, arising into short, triangular, slightly prominent wings. Abdomen prolonged into a cylindrical, narrow tube of the same length as the thorax. Terminal mouth very narrow. Pores subregular, circular.
Dimensions.—Length of the three joints, a 0.03, b 0.12, c 0.12; breadth, a 0.03, b 0.09, c 0.03.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms.
13. Pterocorys pipetta, n. sp.
Shell thin-walled, smooth, with two slight strictures. Length of the three joints = 1 : 6 : 3, breadth = 1 : 3 : 1. Cephalis ovate, with a conical horn of twice the length. Thorax ovate, in the middle zone with three conical wings of the same length, curved slightly downwards (like those of Pterocorys columba, Pl. 71, fig. 2). Abdomen constricted into a cylindrical tube half as long as the thorax, with narrow mouth. Pores subregular, circular.
Dimensions.—Length of the three joints, a 0.02, b 0.12, c 0.06; breadth, a 0.02, b 0.06, c 0.02.
Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.
Definition.—Horn of the cephalis double or multiple. Abdomen not prolonged into a narrow tube.
14. Pterocorys rhinoceros, n. sp. (Pl. 71, fig. 1).
Shell very delicate and thin-walled, with two sharp strictures. Length of the three joints = 2 : 10 : 3, breadth, 3 : 11 : 9. Cephalis obtuse, conical, with two divergent, conical horns of equal length. Thorax triangular, pyramidal; from its three edges there arise on the middle joint three conical descending wings (little larger than the horns), and from the base of each wing descend two divergent crests, forming at the sides of the pyramid three rounded lobes. Abdomen short, cylindrical, with wide, truncate mouth. Network of the whole shell very delicate, with very small and numerous, regular, circular, hexagonally-framed pores.
Dimensions.—Length of the three joints, a 0.02, b 0.1, c 0.03; breadth, a 0.03, b 0.11, c 0.09.
Habitat.—Central Pacific, Stations 270 to 274, surface, and in various depths.
15. Pterocorys prismatica, n. sp.
Shell very delicate and thin-walled throughout, with fine fenestration similar to that of the preceding species, but differing from it in the form of the abdomen, which is much larger, three-sided and prismatic; three edges of the prism decurrent from the bases of the three short wings. Length of the three joints = 1 : 4 : 5, breadth = 2 : 6 : 6. No lobes at the thorax. Mouth wide open, truncate, triangular.
Dimensions.—Length of the three joints, a 0.02, b 0.08, c 0.1; breadth, a 0.04, b 0.12, c 0.12.
Habitat.—South Pacific, Station 288, surface.
16. Pterocorys tricornis, n. sp.
Shell spiny, with two deep strictures. Length of the three joints = 1 : 5 : 3, breadth = 1 : 7 : 5. Cephalis subspherical, with three stout, pyramidal, divergent horns, which are three times as long, and bear three serrated edges. Thorax three-sided pyramidal, spiny; its three edges prolonged at the girdle into three stout, triangular, prismatic wings of the same length, little curved. Abdomen short, cylindrical, with wide open, truncate mouth. Pores irregular, polygonal, roundish.
Dimensions.—Length of the three joints, a 0.02, b 0.1, c 0.06; breadth, a 0.03, b 0.14, c 0.1.
Habitat.—North Pacific, Station 244, surface.
17. Pterocorys zittelii, Haeckel.
Pterocyrtidium zittelii, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. pp. 531, 540, Taf. xxxiii. figs. 28, a, b.
Shell thin-walled, rough, with two slight strictures. Length of the three joints = 2 : 5 : 7, breadth = 3 : 5 : 5. Cephalis hemispherical, armed with a very large, prismatic, vertical horn, which is half as long as the shell, and at its base surrounded by several (three to five) shorter, upwardly diverging horns. Thorax campanulate, in the upper half with three short, downwardly diverging, conical wings. Abdomen subcylindrical, with wide, truncate mouth. Pores small, subregular, circular.
Dimensions.—Length of the three joints, a 0.02, b 0.05, c 0.07; breadth, a 0.03, b 0.05, c 0.05.
Habitat.—Fossil in Barbados.
18. Pterocorys macroptera, n. sp.
Shell thin-walled, smooth, with two slight strictures. Length of the three joints = 1 : 3 : 2, breadth = 1 : 4 : 3. Cephalis hemispherical, armed with two larger and six to eight smaller, conical, divergent horns of different lengths. Thorax three-sided pyramidal; its three edges prolonged into three very large diverging wings, which are slender, three-sided, prismatic, and nearly twice as long as the shell. Abdomen short, cylindrical, with wide, truncate mouth. Pores irregular, roundish, in the middle part of the shell (on both sides of the girdle) much larger than in the upper and lower part.
Dimensions.—Length of the three joints, a 0.03, b 0.09, c 0.06; breadth, a 0.04, b 0.12. c 0.1.
Habitat.—South Atlantic, Station 335, surface.
Definition.—Theopilida (vel Tricyrtida triradiata aperta) with three lateral ribs enclosed in the wall of the thorax, without free lateral or terminal appendages.
The genus Theopilium differs from all the other Theopilida in the absence of free external appendages; it has neither lateral wings nor terminal feet, but three divergent ribs are enclosed in the wall of the thorax. It agrees in this character with the Dicyrtid Lamprodiscus, and may be derived directly from this by development of an abdomen.
1. Theopilium tricostatum, n. sp. (Pl. 70, fig. 6).
Shell flatly conical, smooth. Length of the three joints = 1 : 4 : 2, breadth = 2 : 6 : 10. Cephalis subspherical, with a thin oblique horn of the same length. Thorax with three stout ribs in its wall, and with subregular, hexagonal pores increasing in size towards the girdle. Abdomen flatter than the thorax, without ribs, nearly horizontal, with subregular, square pores, disposed in four to six concentric, subcircular series of different sizes; decreasing in size towards the wide open mouth. Seen from the side, this species resembles Corocalyptra agnesæ, (Pl. 59, fig. 3).
Dimensions.—Length of the three joints, a 0.02, b 0.08, c 0.04; breadth, a 0.03, b 0.12, c 0.2.
Habitat.—Central Pacific, Stations 260 to 274, surface.
2. Theopilium triradiatum, n. sp.
Shell flatly conical, smooth, in general of the same form as, and with similar fenestration to, the preceding species, but different in the proportions. Length of the three joints = 1 : 4 : 2, breadth = 2 : 4 : 6. Cephalis hemispherical, with two divergent, thin horns of the same length. Thorax more elevated, about as high as broad. The three divergent ribs are not limited to the thorax, but prolonged through the whole abdomen, the outline of which is a prolongation of that of the thorax.
Dimensions.—Length of the three joints, a 0.025, b 0.1, c 0.05; breadth, a 0.05, b 0.1, c 0.15.
Habitat.—Tropical Atlantic, Station 347, surface.
3. Theopilium cranoides, Haeckel.
Eucyrtidium cranoides, Haeckel, 1862, Monogr. d. Radiol., p. 320, Taf. vii. figs. 1-3.
Shell campanulate-conical, smooth. Length of the three joints = 2 : 5 : 4, breadth = 3 : 9 : 10. Cephalis ovate, with a straight, excentric, prismatic horn of the same length. The campanulate thorax is separated from it by no external collar stricture, but by an internal septum. From the base of the horn arise three divergent radial ribs, running in the wall of the two first joints to the lumbar stricture (loc. cit., Taf. vii. fig. 3). Abdomen short and wide, without ribs. Pores rather large, regular, circular, quincuncial, in the cephalis smaller. Central capsule four-lobed.
Dimensions.—Length of the three joints, a 0.027, b 0.054, c 0.047; breadth, a 0.03, b 0.09, c 0.1.
Habitat.—Mediterranean (Messina), surface.
Definition.—Theopilida (vel Tricyrtida triradiata aperta) with three simple, free, lateral wings, arising from the collar stricture between cephalis and thorax.
The genus Corocalyptra comprises a small number of very elegant hat-shaped Tricyrtida, which resemble greatly Eucecryphalus among the Dicyrtida. As in the latter, three free, radial spines, or simple wings, corresponding to the three basal feet of Cortina, arise from the collar stricture between the small hemispherical cephalis and the large, flatly conical thorax. Corocalyptra differs from Eucecryphalus, its ancestral form, in the development of a flat and broad abdomen, which is a prolongation of the thorax, and may be compared to the brim of a hat.
1. Corocalyptra agnesæ, n. sp. (Pl. 59, fig. 3).
Shell flatly conical or hat-shaped. Length of the three joints = 1 : 4 : 2, breadth = 2 : 8 : 12. Cephalis hemispherical, with an oblique, small, conical horn of the same length. From the slight collar stricture arise three slender, conical feet of equal length, twice as long as the apical horn, nearly horizontally divergent. Lateral outline of the conical thorax straight, of the flatter abdomen convex; the smooth margin of the abdomen turned inwards. Network delicate, with subregular, hexagonal pores.
Dimensions.—Length of the three joints, a 0.02, b 0.08, c 0.04; breadth, a 0.03, b 0.15, c 0.24.
Habitat.—Central Pacific, Station 270, surface.
2. Corocalyptra elisabethæ, n. sp. (Pl. 59, fig. 10).
Shell flatly conical, hat-shaped, very similar to the preceding species, but with different proportions. Length of the three joints = 1 : 4 : 2; breadth = 1 : 7 : 10. Cephalis very small, with an oblique horn of the same length. The three feet are of different sizes, the caudal odd foot being twice as long as the two lateral, which are equal to the horn. Lateral outline of the campanulate thorax convex, of the flatter abdomen less convex. Margin of the mouth flat.
Dimensions.—Length of the three joints, a 0.015, b 0.06, c 0.03; breadth a 0.02, b 0.14, c 0.2.
Habitat.—Tropical Atlantic, Station 347, surface.
3. Corocalyptra emmæ, n. sp. (Pl. 59, fig. 4).
Shell nearly conical, hat-shaped. Length of the three joints = 1 : 3 : 1, breadth = 1 : 5 : 7. Cephalis hemispherical, with a straight horn of the same length. Feet of the collar larger than in the preceding species, the two lateral smaller being directed upwards, the larger odd caudal downwards. Thorax slightly campanulate; its hexagonal meshes two to four times as large as those of the short, convex abdomen, which is turned inwards.
Dimensions.—Length of the three joints, a 0.02, b 0.09, c 0.03; breadth, a 0.025, b 0.13, c 0.17.
Habitat.—Central Pacific, Station 273, surface.
4. Corocalyptra margarethæ, n. sp.
Shell nearly conical, hat-shaped, very similar to the preceding species, but with much more delicate hexagonal network, with thread-like bars. Length of the three joints = 1 : 7 : 2, breadth = 1 : 10 : 12. Cephalis hemispherical, with six bristle-shaped spines of half the length of the shell; three horns divergent upwards, and three alternating feet divergent downwards. Thorax nearly conical. Abdomen flatter.
Dimensions.—Length of the three joints, a 0.015, b 0.1, c 0.03; breadth, a 0.02, b 0.15, c 0.18.
Habitat.—North Pacific, Station 236, surface.
5. Corocalyptra ludovicæ, n. sp.
Shell flatly campanulate or hat-shaped. Length of the three joints = 1 : 4 : 3, breadth = 2 : 7 : 10. Cephalis hemispherical, with six bristle-shaped spines, about one-fourth to one-third as long as the shell; three horns diverging upwards, and three alternate feet diverging downwards. Thorax nearly conical. Abdomen much larger than in all preceding species, inflated, with convex, lateral outline; its mouth-edge curved inwards. The network is much finer than in the similar Corocalyptra emmæ (Pl. 59, fig. 4), and the abdomen is relatively twice as long and broad.
Dimensions.—Length of the three joints, a 0.02, b 0.08, c 0.06; breadth, a 0.04, b 0.14, c 0.2.
Habitat.—Central Pacific, Station 271, surface.
Definition.—Theopilida (vel Tricyrtida triradiata aperta) with three latticed free lateral wings on the sides of the thorax, which are not prolonged into the cephalis.
The genus Dictyoceras and the following Pteropilium agree with the two preceding genera in the possession of three lateral wings on the sides of the thorax; but whilst these in the latter are simple solid spines, they are in the former vertical fenestrated plates. Dictyoceras may be derived from Pterocorys by development of a vertical lattice-plate between the thorax and the three free lateral spines arising from it.
1. Dictyoceras insectum, n. sp. (Pl. 71, figs. 6, 7).
Shell with two distinct strictures. Length of the three joints = 1 : 3 : 2, breadth = 2 : 4 : 3. Cephalis hemispherical, with a slender pyramidal horn of twice the length. Thorax subspherical, in the upper half with three divergent lattice-wings of the same length, each of which represents a slender, fenestrated, three-sided pyramid. Abdomen subovate, with wide, truncate mouth (in the figured specimen broken off). Pores circular, small, of different sizes.
Dimensions.—Length of the three joints, a 0.025, b 0.055, c 0.04; breadth, a 0.035, b 0.08, c 0.06.
Habitat.—Central Pacific, Stations 263 to 274, depth 2350 to 2925 fathoms.
2. Dictyoceras formica, n. sp. (Pl. 71, fig. 8).
Shell with obliterate collar, but deep lumbar stricture. Length of the three joints = 1 : 2 : 3, breadth = 2 : 5 : 4. Cephalis conical, with an oblique curved horn of the same length. Thorax with three vaulted swellings between the three prominent, diverging lattice-wings, the apex of which is prolonged downwards into a solid curved spine, half as long as the inflated abdomen. Mouth little constricted. Pores irregular, roundish, of different sizes.
Dimensions.—Length of the three joints, a 0.02, b 0.04, c 0.06; breadth, a 0.03, b 0.1, c 0.09.
Habitat.—North Atlantic, Station 353, surface.
3. Dictyoceras melitta, n. sp. (Pl. 71, fig. 9).
Shell with two deep strictures. Length of the three joints = 1 : 3 : 4, breadth = 1 : 6 : 5. Cephalis subspherical, with two conical divergent horns of the same length. Thorax three-sided pyramidal, the three edges prolonged into three lattice-wings of the same form, with short, terminal spines. Abdomen inflated, subovate, with constricted mouth. Pores small, regular, circular, of equal size, with very thin bars.
Dimensions.—Length of the three joints, a 0.03, b 0.09, c 0.12; breadth, a 0.04, b 0.18, c 0.15.
Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.
4. Dictyoceras bombus, n. sp. (Pl. 71, fig. 10).
Shell with deep collar, but evanescent lumbar stricture. Length of the three joints = 1 : 5 : 3, breadth = 1 : 6 : 7. Cephalis subspherical, with a conical horn of the same length. Thorax campanulate, with three short and broad, triangular lattice-wings, the upper edge of which is nearly horizontal, the lower nearly vertical and decurrent from the height of the collar to the lumbar stricture. Abdomen inflated, with constricted mouth of half the breadth. Pores small, subregular, circular, of nearly equal size.
Dimensions.—Length of the three joints, a 0.02, b 0.1, c 0.06; breadth, a 0.025, b 0.12, c 0.14.
Habitat.—Central Pacific, Station 272, depth 2600 fathoms.
5. Dictyoceras virchowii, Haeckel.
Dictyoceras virchowii, Haeckel, 1862, Monogr. d. Radiol., p. 333, Taf. viii. figs. 1-5.
Lithornithium dictyoceras, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, 1860, p. 840.
Shell with two distinct strictures. Length of the three joints = 1 : 3 : 4, breadth = 1 : 5 : 6. Cephalis subspherical, with an oblique curved horn of the same length. Thorax conical, with three broad, triangular lattice-wings different in size and direction, two of which are directed outwards, the third downwards—each terminated by a strong spine. Abdomen oblique, inflated, with wide open, truncate mouth. On the shell surface some few conical spines are scattered. Pores irregular, roundish, of different sizes. On the peculiar symmetry of this remarkable form, compare the detailed description in my Monograph.
Dimensions.—Length of the three joints, a 0.02, b 0.06, c 0.08; breadth, a 0.02, b 0.1, c 0.12.
Habitat.—Mediterranean, Messina, surface.
Definition.—Theopilida (vel Tricyrtida triradiata aperta) with three latticed free lateral wings on the sides of the thorax, prolonged into the horn of the cephalis in the form of three vertical, free cephalic wings.
The genus Pteropilium differs from the preceding closely allied Dictyoceras in the development of three free, vertical, latticed cephalic wings, expanded between the apical horn of the cephalis and the three wings of the thorax; they may be direct prolongations of the latter. Pteropilium, however, may also be derived directly from the Dicyrtida Callimitra or Clathrocorys by development of an abdomen. All these interesting forms are closely allied to the Plectoidea.
Definition.—Thorax completely latticed, without three larger lateral holes between the three wings.
1. Pteropilium stratiotes, n. sp. (Pl. 70, figs. 9, 10).
Shell thin-walled, with two deep strictures. Length of the three joints = 1 : 5 : 4, breadth = 2 : 6 : 9. Cephalis hemispherical, with a vertical, straight, prismatic horn of three times the length. Thorax inflated, oblique, with three slender, nearly straight, widely divergent ribs, beginning from the collar stricture and united in its centre with the centripetal prolongation of the horn. The basal half of the three ribs is enclosed in the thorax wall, whilst the distal half lies outside it, and is connected with its lower half only by two divergent, reticulated wings. The upper edge of the ribs is connected with the occipital horn by a vertical, loosely reticulated, triangular wing. Abdomen half as long as the thorax, also of irregular and oblique form, with knee-shaped outline and a wide, truncate mouth. Network with irregular polygonal, for the most part quadrangular, meshes, separated by thin bars and forming irregular transverse rows. Some stronger, vein-like ribs ramify in the wall, diverging towards the mouth.
Dimensions.—Length of the three joints, a 0.03, b 0.1, c 0.08; breadth, a 0.04, b 0.12, c 0.18.
Habitat.—Central Pacific, Station 271, surface.
2. Pteropilium hoplites, n. sp.
Shell in the general form and in the irregular, quadrangular fenestration similar to the preceding species, but more heavy and with different proportions. Length of the three joints = 1 : 6 : 4, breadth = 2 : 6 : 8. Cephalis twice as broad as in Pteropilium stratiotes. Thorax more slender and subovate. Abdomen truncate, conical, gradually dilated, with straight, non-geniculate outline. Network coarser, with larger square meshes and thicker bars.
Dimensions.—Length of the three joints, a 0.03, b 0.12, c 0.08; breadth, a 0.05, b 0.12, c 0.16.
Habitat.—Central Pacific, Station 272, depth 2600 fathoms.
3. Pteropilium eques, n. sp.
Shell in the general form and in the irregular, quadrangular fenestration similar to those of the two preceding species, but more slender and with different proportions. Length of the three joints = 1 : 3 : 2, breadth = 2 : 4 : 4. Cephalis flatter. Thorax subconical, also flatter. Abdomen short, cylindrical, with straight outline. Network looser than in the two preceding species, with larger square meshes and thinner bars.
Dimensions.—Length of the three joints, a 0.03, b 0.08, c 0.06; breadth a 0.06, b 0.12, c 0.12.
Habitat.—Central Pacific, Station 274, depth 2750 fathoms.
Definition.—Thorax with three large lateral holes between the three latticed wings.
4. Pteropilium clathrocanium, n. sp. (Pl. 64, fig. 7).
Arachnopilium clathrocanium, Haeckel, Prodromus, 1881, p. 435.
Shell very delicate, with two deep strictures. Length of the three joints = 2 : 4 : 2, breadth = 2 : 10 : 5. Cephalis subspherical, with circular, polygonally-framed pores, and a central, three-sided pyramidal, apical horn of twice the length. Thorax three-sided pyramidal, with three large, ovate holes between three prominent latticed wings. From its surface arises a very delicate, arachnoidal network with irregular, polygonal meshes, enveloping also the entire cephalis. Abdomen wide and short, as long as the cephalis, and half as broad as the distance of the wings, twice as broad as the constricted mouth.
Dimensions.—Length of the three joints, a 0.04, b 0.08, c 0.04; breadth, a 0.05, b 0.2, c 0.1.
Habitat.—Central Pacific, Station 271, depth 2425 fathoms.
Definition.—Theopilida (vel Tricyrtida triradiata aperta) with three divergent solid ribs, which lie in the wall of the thorax and the abdomen, and are prolonged into three solid terminal feet.
The genus Theopodium and the following closely allied Pterocanium differ from the preceding four genera in the development of the three radial rods or the primary cortinar spines, which are not free lateral wings, but longitudinal ribs enclosed in the wall of the thorax and abdomen, and prolonged over the basal mouth into three free terminal feet. These are solid in Theopodium, which, therefore, corresponds to Lychnocanium among the Dicyrtida.
1. Theopodium tricostatum, n. sp. (Pl. 97, fig. 14).
Shell three-sided pyramidal, thorny, with two distinct strictures. Length of the three joints = 1 : 2 : 2, breadth = 1 : 3 : 4. Cephalis hemispherical, with a stout conical horn of the same length. Thorax with regular, circular, hexagonally-framed pores. Abdomen with irregular, roundish pores of very different sizes. From the middle part of the thorax arise the three prominent, wing-like edges of the pyramid, which are prolonged over its wide mouth into three stout, pyramidal, divergent feet about as long as the thorax, with dentate, lamellar edges.
Dimensions.—Length of the three joints, a 0.02, b 0.07, c 0.06; breadth, a 0.04, b 0.09, c 0.12.
Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.
2. Theopodium pyramidale, n. sp.
Shell three-sided pyramidal, rough, without external strictures, but with two broad internal girdles. Length of the three joints = 1 : 2 : 6, breadth = 2 : 4 : 8. Cephalis with a thick horn of the same length, conical. Thorax with very small, regular, circular pores. Abdomen with irregular, roundish pores of very different sizes. From the collar stricture arise the three rectilinear edges of the pyramid, which are prolonged over its wide-open mouth into three stout, divergent, pyramidal feet, about as long as the thorax.
Dimensions.—Length of the three joints, a 0.02, b 0.04, c 0.12; breadth, a 0.04, b 0.075, c 0.15.
Habitat.—Fossil in Barbados.
Definition.—Theopilida (vel Tricyrtida triradiata aperta) with three divergent ribs, which run along the thorax and abdomen, and are prolonged into three latticed terminal feet.
The genus Pterocanium differs from the preceding Theopodium in the fenestration of the three terminal feet, which are basal prolongations of the three radial ribs, enclosed in the wall of the thorax and the abdomen. Often also these ribs are partly or wholly fenestrated. It corresponds to Lychnodictyum among the Dicyrtida, and may be derived from this by development of an abdomen. The latter forms sometimes three concave bays, at other times three convex lobes between the three latticed feet.
Definition.—Free basal edge of the abdomen between the three feet concave, forming three shallower or deeper bays between them.
1. Pterocanium proserpinæ, Ehrenberg.