Definition.—Tripocyrtida, with the basal mouth of the shell open (vel Dicyrtida triradiata aperta).
Definition.—Sethopilida (vel Dicyrtida triradiata aperta) with three complete thoracic ribs, prolonged into three solid divergent feet on the peristome. Cephalis with an apical horn.
The genus Dictyophimus, comprising many common species, may be regarded as the common ancestral form of all sethopilida, and therefore also of the whole family of Dicyrtida. The cephalis bears an apical horn, and the thorax three ribs, which are prolonged over the open mouth into three solid feet. Dictyophimus may be derived either from Euscenium or Peridium (Archiperida), or from Tripospyris (Zygospyrida), or from Plectaniscus (Plectanida), by development of lattice-work between the three terminal feet, which therefore become thoracic ribs.
Definition.—Shell smooth or rough, without prominent spines on the edges of the three thoracic ribs. (Commonly one single horn on the cephalis.)
1. Dictyophimus sphærocephalus, n. sp. (Pl. 57, fig. 10).
Shell smooth, with a deep collar stricture, separating two joints of nearly equal size. Cephalis subglobular, rough, with a stout pyramidal horn of half the length, and regular, circular, hexagonally framed pores. Thorax nearly three-sided prismatic, smooth, with three stout, little divergent or nearly parallel ribs, which are prolonged into conical subvertical feet half as long. Thoracic pores irregular, roundish.
Dimensions.—Cephalis 0.08 long, 0.08 broad; thorax 0.08 long, 0.08 broad.
Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.
2. Dictyophimus tripus, Haeckel.
Dictyophimus tripus, Haeckel, 1862, Monogr. d. Radiol., p. 306, Taf. vi. fig. 1.
Shell with a slight collar stricture, separating two joints of slightly different size. Cephalis nearly ellipsoidal, large, with a slender conical horn of the same length. Thorax truncate three-sided pyramidal, with three strongly divergent ribs, which are prolonged into three slender conical feet of about the same length. Pores irregular, roundish, of variable size.
Dimensions.—Cephalis 0.032 long, 0.028 broad; thorax 0.34 long, 0.064 broad.
Habitat.—Mediterranean (Messina), Atlantic (Canary Islands), surface.
3. Dictyophimus plectaniscus, n. sp. (Pl. 61, figs. 8, 9).
Shell flat, pyramidal, smooth, with distinct collar stricture. Cephalis hemispherical, with a conical horn of the same length and numerous small regular pores. Thorax flat, triangular, pyramidal, with three widely divergent ribs, which are prolonged into three cylindrical feet of the same length. Thoracic pores fifteen, very large, subregular, roundish, disposed in two transverse girdles, the inner with six, the outer with nine pores; five pores between every two ribs.
Dimensions.—Cephalis 0.04 long, 0.06 broad; thorax 0.08 long, 0.18 broad.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms.
4. Dictyophimus craticula, Ehrenberg.
Dictyophimus craticula, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 68, Taf. v. figs. 4, 5.
Dictyophimus craticula, Bütschli, 1882, Zeitschr. f. Wiss. Zool., vol. xxxvi. p. 515, Taf. xxxiii. fig. 35.
Shell flat, pyramidal, very similar to the preceding species, but differing in the rudimentary horn, which is smaller than half the cephalis, and in the length of the three cylindrical feet, which are twice to three times as long as the shell. The nine inferior large pores of the thorax are twice to three times as large as the six superior pores. The basal peristome is commonly thorny.
Dimensions.—Cephalis 0.04 long, 0.05 broad; thorax 0.1 long, 0.2 broad.
Habitat.—Fossil in Barbados.
5. Dictyophimus pyramis, n. sp. (Pl. 61, fig. 16).
Shell regular, pyramidal, with flat collar stricture. Relative length of the two joints = 1 : 4, breadth = 2 : 6. Cephalis hemispherical, with a stout pyramidal horn of the same length. Thorax triangular pyramidal, with three prominent ribs, which are prolonged into three slender pyramidal feet, half as long. Pores small and very numerous, subregular, circular.
Dimensions.—Cephalis 0.03 long, 0.05 broad; thorax 0.1 long, 0.15 broad.
Habitat.—Central Pacific, Station 266, depth 2750 fathoms.
6. Dictyophimus challengeri, Haeckel.
Dictyophimus challengeri, Haeckel, 1878, Protistenreich, p. 47, fig. 35.
Shell campanulate, with sharp collar stricture. Relative length of the joints = 1 : 3, breadth = 1 : 4. Cephalis subspherical, with a stout pyramidal horn of twice the length, and numerous very small pores. Thorax nearly hemispherical, with three vaulted bosoms between the three decurrent ribs, which are prolonged into three nearly parallel and vertical feet of about the same length. Pores subregular, circular, of medium size. This species is very similar to Lychnodictyum challengeri, Haeckel, but differs in the smaller straight horn and the longer solid feet, which are not fenestrated.
Dimensions.—Cephalis 0.03 long, 0.04 broad; thorax 0.09 long, 0.13 broad.
Habitat.—Tropical Atlantic, Station 347, surface.
7. Dictyophimus lasanum, n. sp. (Pl. 61, fig. 5).
Shell nearly pear-shaped, with distinct collar stricture. Relative length of the two joints = 1 : 3, breadth = 1 : 3. Cephalis hemispherical, with a conical horn of the same length. Thorax nearly spherical, on both poles truncate and constricted, with three decurrent curved ribs and small regular circular pores. The prolongations of the ribs form three divergent pyramidal straight feet, nearly as long as the thorax.
Dimensions.—Cephalis 0.02 long, 0.03 broad; thorax 0.09 long, 0.09 broad.
Habitat.—South Atlantic, Station 332, depth 2200 fathoms.
8. Dictyophimus longipes, n. sp. (Pl. 61, fig. 3).
Shell three-sided pyramidal, with distinct collar stricture. Relative length of the two joints = 1 : 4, breadth = 2 : 6. Cephalis hemispherical, with a rudimentary pyramidal horn, scarcely one-fourth as long; and with small circular regular pores. Thorax with larger irregular pores, and three vaulted bosoms between the three decurrent ribs, which are prolonged into three very long and slender prismatic feet, S-shaped, curved, and twice to three times as long as the shell.
Dimensions.—Cephalis 0.02 long, 0.04 broad; thorax 0.09 long, 0.13 broad.
Habitat.—South Pacific, Station 300, depth 1375 fathoms.
9. Dictyophimus gracilipes, Bailey.
Dictyophimus gracilipes, Bailey, 1856, Amer. Journ. Sci. and Arts, vol. xxii. p. 4, pl. i. fig. 8.
Shell three-sided pyramidal, with a deep collar stricture. Relative length of the two joints = 1 : 3, breadth = 1 : 4. Cephalis hemispherical, with a thin horn of the same length. Thorax with three curved ribs, which are prolonged into three divergent angular feet of the same length. Pores irregular roundish.
Dimensions.—Cephalis 0.02 long, 0.03 broad; thorax 0.05 long, 0.08 broad.
Habitat.—North Pacific, Station 240, surface, Kamtschatka (Bailey).
10. Dictyophimus cortina, n. sp. (Pl. 61, fig. 1).
Shell three-sided pyramidal, with distinct collar stricture. Relative length of the two joints = 1 : 3, breadth = 1 : 4. Cephalis subspherical, with a pyramidal horn of half the length. Thorax with much larger irregular roundish pores and three prominent ribs, which are prolonged into three stout, club-shaped, strongly divergent feet of the same length. Mouth widely open, elegantly coronate, with a circle of numerous small cilia.
Dimensions.—Cephalis 0.02 long, 0.03 broad; thorax 0.06 long, 0.08 broad.
Habitat.—Central Pacific, Station 272, depth 2600 fathoms.
11. Dictyophimus arabicus, Haeckel.
Lychnocanium arabicum, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 296, Taf. x. fig. 3.
Shell smooth, three-sided pyramidal, with deep collar stricture. Relative length of the two joints = 1 : 3, breadth = 1 : 4. Cephalis subspherical, with a slender horn of the same length. Thorax with much larger, irregular roundish pores, and three widely divergent ribs, which are prolonged into three slender, somewhat recurved feet of about the same length.
Dimensions.—Cephalis 0.02 long, 0.02 broad; thorax 0.07 long, 0.09 broad.
Habitat.—Indian Ocean, Zanzibar (Pullen), depth 2200 fathoms.
12. Dictyophimus platycephalus, n. sp. (Pl. 60, figs. 4, 5).
Shell smooth, flat, three-sided pyramidal, with distinct collar stricture. Relative length of the two joints = 1 : 3, breadth = 3 : 9. Cephalis flat, cap-shaped, three times as broad as long, with a slender conical horn of the same length. Thorax flatly vaulted, with much larger, irregular roundish, double-edged pores, and three widely divergent ribs, which are prolonged into three slender conical feet of the same length. Central capsule in the cephalis flat, discoidal, with a discoidal nucleus of half the size, and with four large pear-shaped cæcal sacs depending into the thorax, each of which contains a large oil globule (fig. 4).
Dimensions.—Cephalis 0.02 long, 0.07 broad; thorax 0.06 long, 0.18 broad.
Habitat.—North Atlantic, Canary Islands (Lanzerote), Haeckel, surface.
13. Dictyophimus brandtii, n. sp. (Pl. 60, fig. 6).
Shell smooth, flat, three-sided pyramidal, with deep collar stricture, very similar to the preceding species. Relative length of the two joints = 1 : 3, breadth = 2 : 7. Cephalis hemispherical, with a slender conical horn of twice the length. Thorax flatly vaulted, with irregular polygonal pores and thin bars; and with three widely divergent ribs, which are prolonged into three slender prismatic feet of thrice the length. In fig. 6 the shell is seen from the base and exhibits very distinctly the collar septum with its four large meshes, two minor jugular and two major cardinal pores.
Dimensions.—Cephalis 0.03 long, 0.07 broad; thorax 0.08 long, 0.2 broad.
Habitat.—North Pacific, Station 236, surface.
14. Dictyophimus lucerna, Haeckel.
Lychnocanium lucerna, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 6; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, p. 80, Taf. viii. fig. 3.
Lychnocanium lucerna, Haeckel, 1862, Monogr. d. Radiol., p. 311.
Shell smooth, three-sided pyramidal, with slight collar stricture. Relative length of the two joints = 1 : 4, breadth = 1 : 4. Cephalis hemispherical, with a thick conical horn of twice the length. Thorax with small regular, circular pores and three flat sides; between these arise three rounded ribs, which are prolonged into three short, conical, divergent feet, one-third as long as the thorax.
Dimensions.—Cephalis 0.02 long, 0.025 broad; thorax 0.08 long, 0.08 broad.
Habitat.—Fossil in Barbados.
15. Dictyophimus hamosus, Haeckel.
Lychnocanium hamosum, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 78, Taf. vii. fig. 9.
Shell pear-shaped, rough, with deep collar stricture. Relative length of the two joints = 1 : 2, breadth = 1 : 3. Cephalis subglobular, with a conical horn of twice the length. Thorax with small, regular, circular pores, and with three prominent ribs, prolonged into three vertical prismatic feet, which are about as long as the shell, parallel or a little convergent towards the distal end, with recurved teeth or hooks at the lateral edges.
Dimensions.—Cephalis 0.02 long, 0.02 broad; thorax 0.04 long, 0.06 broad.
Habitat.—Fossil in Barbados.
16. Dictyophimus tridentatus, Haeckel.
Lychnocanium tridentatum, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 80, Taf. vii. fig. 4.
Shell smooth, three-sided pyramidal, with deep collar stricture. Relative length of the two joints = 1 : 3, breadth = 1 : 4. Cephalis subspherical, with a conical horn of the same length, and some small accessory thorns. Thorax tetrahedral, with three smooth hyaline walls, bearing only a single series of small pores on each side of the three prominent ribs, which are prolonged into three strong prismatic curved feet of twice the length, with the convexity external. A group of small pores and a strong triangular tooth at the base of each foot.
Dimensions.—Cephalis 0.02 long, 0.02 broad; thorax 0.06 long, 0.08 broad.
Habitat.—Fossil in Barbados.
Definition.—Shell spiny or thorny, with prominent spines on the edges of the three thoracic ribs. (Commonly one larger and a few smaller horns or spines on the cephalis.)
17. Dictyophimus triserratus, n. sp. (Pl. 61, fig. 17).
Shell three-sided pyramidal, with slight collar stricture. Relative length of the two joints = 1 : 3, breadth = 1 : 4. Cephalis small, subspherical, with a large pyramidal horn three times as long. Thorax with much larger, irregular roundish, double-edged pores, and three prominent, serrate ribs, which are prolonged into three pyramidal strongly divergent feet of the same length.
Dimensions.—Cephalis 0.02 long, 0.02 broad; thorax 0.06 long, 0.09 broad.
Habitat.—Central Pacific, Station 274, depth 2750 fathoms.
18. Dictyophimus bicornis, n. sp.
Shell thorny, with deep collar stricture. Relative length of the two joints = 2 : 3, breadth = 2 : 3. Cephalis nearly as large as the thorax, subglobular, with numerous small, circular pores, and two divergent pyramidal horns of half the length (a major occipital and a minor frontal horn). Thorax three-sided pyramidal, with larger irregular pores and three serrate ribs, which are prolonged into three prismatic spiny feet of half the length. (Differs from the similar Dictyophimus sphærocephalus, Pl. 57, fig. 10, mainly in the double horn and the spinulate feet.)
Dimensions.—Cephalis 0.05 long, 0.05 broad; thorax 0.08 long, 0.07 broad.
Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.
19. Dictyophimus pocillum, Ehrenberg.
Dictyophimus pocillum, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 68, Taf. v. fig. 6.
Shell thorny, with distinct collar stricture. Relative length of the two joints = 1 : 5, breadth = 1 : 5. Cephalis nearly spherical, with numerous small conical spines. Thorax flat, three-sided pyramidal with large, irregular, roundish pores, and three strong, widely divergent, spinulate ribs, which are prolonged into three prismatic spinulate feet of the same length.
Dimensions.—Cephalis 0.03 long, 0.03 broad; thorax 0.15 long, 0.15 broad.
Habitat.—Fossil in Barbados.
20. Dictyophimus cienkowskii, n. sp. (Pl. 60, fig. 1).
Lamprotripus squarrosus, Haeckel, 1881, Prodromus et Atlas.
Shell spiny, flatly pyramidal, with slight collar stricture. Relative length of the two joints = 1 : 3, breadth = 2 : 6. Cephalis flat, cap-shaped, three times as long as broad, with numerous bristle-shaped spines three times as long. Thorax also spiny, with irregular, very large, polygonal meshes and thin bars; its three ribs prolonged into three very long and thin, widely divergent, prismatic feet, bearing numerous long spines on the three edges.
Dimensions.—Cephalis 0.025 long, 0.05 broad; thorax 0.075 long, 0.15 broad.
Habitat.—North Pacific, Station 250, surface.
21. Dictyophimus bütschlii, n. sp. (Pl. 60, fig. 2).
Lamprotripus horridus, Haeckel, 1881, Prodromus et Atlas.
Shell spiny, flatly pyramidal, with deep collar stricture. Relative length at the two joints = 1 : 2, breadth = 1 : 5. Cephalis subspherical, with numerous long, bristle-shaped spines and a larger ramified horn. Thorax also spiny, flatly vaulted, with large, subregular, hexagonal meshes and thin bars; its three spiny ribs prolonged into three very long and thin, prismatic, widely divergent feet, twice to four times as long as the thorax.
Dimensions.—Cephalis 0.04 long, 0.04 broad; thorax 0.08 long, 0.2 broad.
Habitat.—South Pacific, Station 284, surface.
22. Dictyophimus hertwigii, n. sp. (Pl. 60, fig. 3).
Lamprotripus spinosus, Haeckel, 1881, Prodromus et Atlas.
Shell spiny, flatly pyramidal with sharp collar stricture. Relative length of the two joints = 1 : 2, breath = 1 : 5. Cephalis subspherical, with irregular roundish pores, numerous small spines and a large, oblique, prismatic horn of the same length, bearing on its distal end a bunch of small divergent spines. Thorax pyramidal, with larger irregular polygonal pores and thin bars; its three strong, widely divergent ribs spiny, straight, and prolonged into three prismatic slender feet of the same length. Central capsule with three lobes depending into the thorax.
Dimensions.—Cephalis 0.04 long, 0.04 broad; thorax 0.08 long, 0.2 broad.
Habitat.—Central Pacific, Stations 270 to 274, surface.
Definition.—Sethopilida (vel Dicyrtida triradiata aperta) with three complete thoracic ribs, prolonged into three latticed divergent feet on the peristome. Cephalis with an apical horn.
The genus Tripocyrtis has been derived from the preceding Dictyophimus by complete fenestration of the three basal feet, which throughout their whole length become united by complete lattice-work. This genus is closely allied to Plectaniscus.
1. Tripocyrtis plagoniscus, n. sp. (Pl. 60, fig. 10).
Cephalis subspherical, with large, roundish meshes and a stout, three-sided pyramidal, irregularly branched horn of twice the length. Thorax with a small number of large, irregular, polygonal meshes and three stout curved ribs about as long as the cephalic horn.
Dimensions.—Cephalis 0.06 long, 0.07 broad; thorax 0.11 long, 0.16 broad.
Habitat.—Central Pacific, Station 266, surface.
2. Tripocyrtis tripodiscus, n. sp.
Cephalis subspherical, with small, polygonal pores and a large, arborescent, vertical horn of thrice the length, bearing numerous ramified branches. Thorax with three straight, widely divergent ribs, of the same length as the horn, connected by a delicate, arachnoidal framework with irregular, polygonal meshes.
Dimensions.—Cephalis 0.04 long, 05 broad; thorax 0.12 long, 0.18 broad.
Habitat.—Central Pacific, Station 269, surface.
3. Tripocyrtis plectaniscus, n. sp. (Pl. 60, fig. 9).
Cephalis subspherical, with small roundish pores, and a stout, three-sided pyramidal, denticulate horn of the same length. Thorax with three little divergent and curved ribs, twice as long as the horn, in the upper half with smaller, in the lower half with larger, polygonal, irregular meshes.
Dimensions.—Cephalis 0.05 long, 0.06 broad; thorax 0.1 long, 0.12 broad.
Habitat.—Central Pacific, Station 264, surface.
Definition.—Sethopilida (vel Dicyrtida triradiata aperta) with three complete thoracic ribs, which are prolonged into three solid divergent feet on the peristome. Cephalis smooth, without a horn.
The genus Sethopilium differs from its probable ancestral form Dictyophimus by the complete loss of the cephalic horn, and of the collar septum between both joints, which are only separated by the slight external collar stricture.
1. Sethopilium orthopus, n. sp. (Pl. 97, fig. 8).
Shell smooth, with sharp collar stricture, Relative length of the two joints = 5 : 4, breadth = 7 : 6. Cephalis large, subspherical, with numerous regular circular pores, twice as broad as the bars. Thorax with three stout, straight, widely divergent ribs, prolonged into three straight pointed feet of the same length. Between every two ribs, in the centre of the collar stricture, a single large triangular mesh, and beyond this three to six rows of smaller irregular meshes.
Dimensions.—Cephalis 0.05 long, 0.07 broad; thorax 0.04 long, 0.06 broad.
Habitat.—Central Pacific, Station 266, depth 2750 fathoms.
2. Sethopilium cyrtopus, n. sp.
Shell smooth, with sharp collar stricture. Relative length of the two joints = 4 : 6, breadth = 7 : 11. Cephalis hemispherical, with large irregular roundish pores, four times as broad as the bars. Thorax with three stout, curved, widely divergent ribs, prolonged into three cylindro-conical, curved feet of twice the length, which are convex in the proximal half, concave in the distal half. Between every two ribs, beyond the collar stricture, two large ovate meshes, and beyond this two rows of smaller irregular meshes.
Dimensions.—Cephalis 0.04 long, 0.07 broad; thorax 0.05 long, 0.11 broad.
Habitat.—Central Pacific, Station 268, depth 2900 fathoms.
3. Sethopilium macropus, n. sp. (Pl. 97, fig. 9).
Shell smooth, with slight collar stricture. Relative length of the two joints = 4 : 7, breadth = 6 : 13. Cephalis hemispherical, with irregular double-contoured pores, about as broad as the bars. Thorax with three very stout, carved, widely divergent ribs, prolonged into three curved, cylindrical, very long feet, which are three to four times as long as the shell, and convex on the outside. Between every two ribs, beyond the collar stricture, two large broad meshes, and beyond this two or three rows of smaller meshes.
Dimensions.—Cephalis 0.04 long, 0.06 broad; thorax 0.07 long, 0.13 broad.
Habitat.—Central Pacific, Station 271, depth 2425 fathoms.
Definition.—Sethopilida (vel Dicyrtida triradiata aperta) with three free lateral wings, or solid spines arising from the sides of the thorax. No terminal feet. Cephalis with one or more horns.
The genus Lithomelissa, containing numerous and widely distributed forms, may like Dictyophimus be regarded as one of the most primitive and ancient forms of Dicyrtida. It differs from the latter by the lateral (not terminal) position of the three thoracic feet, and may be derived either from Dictyophimus (by secondary development of intrapedal network towards the mouth, on the inside of the three feet) or directly from Tripospyris by similar formation of thoracic network beyond the collar stricture, outside the base of the three divergent feet and pierced by the latter. As the species of this genus are numerous, it may perhaps be better to divide it into two or three genera: Acromelissa, with a single horn, Micromelissa, with two horns, and Sethomelissa, with three or more horns.
Definition.—Cephalis with a single occipital horn.
1. Lithomelissa macroptera, Ehrenberg.
Lithomelissa macroptera, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 78, Taf. iii. figs. 9, 10.
Shell smooth, with distinct collar stricture. Relative length of the two joints = 4 : 5, breadth = 3 : 4. Cephalis ovate, with a stout, excentric, vertical, pyramidal horn of the same length. Thorax little larger, ovate, truncate. Both joints with very small and scattered pores. Three divergent ribs arise from the base of the cephalic horn, and are prolonged over the major part of the thorax; their under free part arises from the middle part of the thorax and is as long as the horn, straight, pyramidal. Mouth truncate, little constricted.
Dimensions.—Cephalis 0.04 long, 0.03 broad; thorax 0.05 long, 0.04 broad.
Habitat.—Fossil in Barbados.
2. Lithomelissa ehrenbergii, Bütschli.
Lithomelissa ehrenbergii, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 517, Taf. xxxiii. fig. 21a, b.
Lithomelissa macroptera, var., Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 78, Taf. iii. fig. 8.
(?) Lophophæna capito, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 78, Taf. viii. fig. 6.
(?) Lophophæna galeata, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 78, Taf. viii. fig. 12.
Shell rough, with distinct collar stricture. Relative length of the two joints = 4 : 2, breadth = 3 : 4. Cephalis ovate, with a stout excentric, oblique, pyramidal horn of half the length. Thorax little shorter, truncate, conical. Both joints with regular circular pores, of the same breadth as the bars. Three divergent conical feet, as long as the cephalis, arise below the collar stricture. Mouth truncate, not constricted.
Dimensions.—Cephalis 0.08 long, 0.06 broad; thorax 0.04 long, 0.08 broad.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms; fossil in Barbados.
3. Lithomelissa macroceras, n. sp.
Shell spiny, with sharp collar stricture. Relative length of the two joints = 5 : 7, breadth = 5 : 6. Cephalis spherical, with a large pyramidal horn of twice the length. Thorax little longer, ovate, truncate. Both joints with regular circular pores, three times as broad as the bars. Three divergent pyramidal feet, twice as long as the cephalis, arise from the middle part of the thorax. Mouth constricted, half as broad as the thorax.
Dimensions.—Cephalis 0.05 long, 0.05 broad; thorax 0.07 long, 0.06 broad.
Habitat.—South Atlantic, Station 332, depth 2200 fathoms.
4. Lithomelissa mitra, Bütschli.
Lithomelissa mitra, Bütschli, 1881, Zeitschr. f. wiss. Zool., p. 518, Taf. xxxiii. fig. 24.
Shell smooth, with distinct collar stricture. Relative length of the two joints = 5 : 4, breadth = 4 : 5. Cephalis ovate, with a slender, straight, vertical, pyramidal horn of the same length. Thorax ovate, truncate, of about the same size. Both joints with very small and numerous pores, as broad as the bars. Three feet arising from the middle part of the thorax, very small, rudimentary, pyramidal, about as long as broad. Mouth truncate, little constricted.
Dimensions.—Cephalis 0.05 long, 0.04 broad; thorax 0.04 long, 0.05 broad.
Habitat.—Fossil in Barbados.
5. Lithomelissa pycnoptera, n. sp.
Shell rough, papillate, with slight collar stricture. Relative length of the two joints = 1 : 3, breadth = 1 : 3. Cephalis small, hemispherical, with very small pores and a slender, straight, conical horn of twice the length. Thorax subconical, with regular circular, hexagonally framed pores, as broad as the bars. From its lower half arise three divergent, very strong feet, pyramidal, as long as the thorax, and three times as long as broad.
Dimensions.—Cephalis 0.03 diameter, thorax 0.1 diameter.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms.
6. Lithomelissa microstoma, n. sp.
Shell papillate, with slight collar stricture. Relative length of the two joints = 1 : 5, breadth = 1 : 5. Cephalis small, hemispherical, with a conical horn of twice the length. Thorax subspherical, with subregular circular pores, three times as broad as the bars. From its middle part arise three divergent, stout, conical feet, of half the length, and twice as long as broad. Mouth small, strongly constricted, one-fourth to one-third as broad as the thorax.
Dimensions.—Cephalis 0.03 long, 0.04 broad; thorax 0.15 diameter.
Habitat.—Fossil in Barbados.
7. Lithomelissa amphora, Stöhr.
Lithomelissa amphora, Stöhr, 1880, Palæontograph, vol. xxvi. p. 100, Taf. iii. fig. 11.
Shell smooth, with sharp collar stricture. Relative length of the two joints = 1 : 5, breadth = 2 : 4. Cephalis small, hemispherical, with a cervical horn of the same length. Thorax ovate, with small regular circular pores, twice as broad as the bars. From its upper half arise three divergent, slender, conical feet, only one-fourth as long. Mouth constricted, with a hyaline peristome, half as broad as the thorax.
Dimensions.—Cephalis 0.013 long, 0.026 broad; thorax 0.063 long, 0.053 broad.
Habitat.—Fossil in tertiary rocks of Sicily; Grotte (Stöhr).
Definition.—Cephalis with two divergent horns, a superior occipital horn and an inferior frontal horn.
8. Lithomelissa thoracites, Haeckel.
Lithomelissa thoracites, Haeckel, 1862, Monogr. d. Radiol., p. 301, Taf. vi. figs. 2-8.
Lithomelissa thoracites, R. Hertwig, 1879, Organism. d. Radiol., p. 76, Taf. viii. fig. 1.
Shell smooth, with deep collar stricture. Cephalis ovate, with two divergent, slender, conical horns, of about half the length; a major oblique occipital horn on the posterior face, and a minor, nearly horizontal horn above the collar stricture, on the anterior face. Thorax about as large as the cephalis, truncate, ovate. Pores of both joints irregular, roundish, of different sizes. From the upper half of the thorax, below the collar stricture, there arise three slender, conical divergent feet, about as long as the cephalis. Mouth truncate, wide open, not constricted. On the numerous varieties of this common species compare my Monograph, on the structure of the ovate central capsule (enclosed in the cephalis), Hertwig, loc. cit.
Dimensions.—Cephalis 0.05 to 0.08 long, 0.04 broad; thorax 0.03 to 0.05 long, 0.05 to 0.07 broad.
Habitat.—Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface.
9. Lithomelissa mediterranea, J. Müller.
Lithomelissa mediterranea, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 45, Taf. vi. fig. 11.
Lithomelissa mediterranea, Haeckel, 1862, Monogr. d. Radiol., p. 302.
Shell smooth, with sharp collar stricture. Relative length of the two joints = 4 : 5, breadth = 4 : 5. Cephalis campanulate, conical, with two divergent small conical horns, a major occipital subvertical horn near the summit, and a minor sub-horizontal frontal horn near the collar stricture. Thorax truncate, ovate, little larger than the cephalis. From its lower part there arise three short conical, divergent feet, scarcely half as long as the cephalis (in Müller's figure one of them is seen shortened, opposite to the frontal horn). Pores irregular, roundish, much smaller in the cephalis than in the thorax. Mouth wide open, not constricted.
Dimensions.—Cephalis 0.04 diameter, thorax 0.05 diameter.
Habitat.—Mediterranean (French shore), J. Müller, surface.
10. Lithomelissa bicornis, Ehrenberg.
Lithomelissa bicornis, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 297, Taf. ii. fig. 7.
Shell smooth, with deep collar stricture. Relative length of the two joints = 1 : 3, breadth = 1 : 2. Cephalis hemispherical, with two divergent, stout and straight, pyramidal horns; a larger occipital horn sub-vertical near the summit, and a smaller oblique frontal horn near the collar stricture. Thorax subspherical, twice as large, with larger irregular, roundish pores. From its lower half there arise three divergent curved pyramidal feet of about the same length. Mouth constricted, only one-third as broad as the thorax.
Dimensions.—Cephalis 0.02 long, 0.03 broad; thorax 0.06 diameter.
Habitat.—Atlantic, Stations 348 to 353, surface.
11. Lithomelissa haeckelii, Bütschli.
Lithomelissa haeckelii, Bütschli, 1883, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 517, Taf. xxxiii. fig. 23, a, b.
Shell rough, with sharp collar stricture. Relative length of the two joints = 6 : 5, breadth = 6 : 7. Cephalis subspherical, large, with two divergent horns, a very large, oblique pyramidal occipital horn on the summit, and a very small frontal horn on the middle of the forehead. Thorax campanulate, little larger than the cephalis, with regular circular pores of twice the breadth. From the upper part of the thorax, below the collar stricture, there arise three stout, divergent, angular, semi-lunar feet, about as long as the shell. Mouth wide open, not constricted.
Dimensions.—Cephalis 0.6 long, 0.6 broad; thorax 0.05 long, 0.07 broad.
Habitat.—Tropical Atlantic, Station 347, depth 2260 fathoms; fossil in Barbados.
12. Lithomelissa bütschlii, n. sp. (Pl. 56, fig. 1).
Shell smooth, with slight collar stricture. Relative length of the two joints = 5 : 6, breadth = 4 : 5. Cephalis ovate, large, with two small conical horns, which are opposed nearly horizontally, in the upper part of the cephalis; an anterior frontal and a posterior occipital horn. Thorax ovate, truncate, little larger. Pores of both joints irregular, roundish, of very different sizes. From the middle part of the thorax there arise three short conical divergent feet. (In the figured specimen there were some accessory thorns; in another specimen, found afterwards, the surface was quite smooth, but the two horns and the three feet much larger, half as long as the cephalis.)
Dimensions.—Cephalis 0.05 long, 0.04 broad; 0.06 long, 0.05 broad.
Habitat.—Central Pacific, Stations 266 to 274, depth 2350 to 2925 fathoms.
Definition.—Cephalis with three, four, or more horns, a primary occipital, a secondary frontal, and one or more accessory parietal horns.
13. Lithomelissa corythium, Ehrenberg.
Lithomelissa corythium, Ehrenberg, 1875, Abhandl. d.k. Akad. d. Wiss. Berlin, p. 78, Taf. iii, fig. 12.
Shell smooth, with slight collar stricture. Relative length of the two joints = 4 : 3, breadth = 4 : 5. Cephalis campanulate, with three short conical horns on the summit. Thorax flat and wide. From its upper part below the collar stricture, there arise three divergent, pyramidal feet, fenestrated at the base, about as long as the shell. Mouth wide open. (The specimen figured by Ehrenberg was an incomplete one.)
Dimensions.—Cephalis 0.04 in diameter, thorax 0.03 long, 0.05 broad.
Habitat.—Central Pacific, Station 268, depth 2900 fathoms; fossil in Barbados.
14. Lithomelissa decacantha, n. sp. (Pl. 56, fig. 2).
Sethomelissa decacantha, Haeckel, 1881, Prodromus et Atlas.
Shell smooth, with deep collar stricture, and with ten prismatic spines of nearly equal size and similar form. Relative length and breadth of the two joints about equal. Cephalis ovate, in the upper half hyaline, in the lower half with few scattered pores; in the equator with four prismatic horns of the same length, which diverge upwards; three of them are placed in the same meridional planes as the three wings and the three feet of the thorax (one occipital and two parietal); the fourth (frontal) horn is opposed to the occipital. Thorax campanulate, three-edged, with three vertical prominent feet (directed downward) and three horizontal wings, arising from their knees. Mouth wide open, not constricted.
Dimensions.—Cephalis 0.05 diameter; thorax 0.05 long, 0.06 broad.
Habitat.—Equatorial Atlantic, Station 347, surface.
Definition.—Sethopilida (vel Dicyrtida triradiata aperta) with three free lateral wings, or solid spines arising from the sides of the thorax. No terminal feet. Cephalis smooth, without a horn.
The genus Psilomelissa has the same formation of the shell as the nearly allied preceding genus Lithomelissa, and may be derived from it by reduction and loss of the cephalic horn. The cephalis is quite bare.
1. Psilomelissa galeata, Haeckel.