Page:Scientific results HMS Challenger vol 18 part 2.djvu/392

1268 Arachnocorys araneosa (Pl. 56, fig. 11), but differing in the structure of the cephalis, and in the greater number of the ribs and spines.

Dimensions.—Cephalis 0.04 diameter, thorax 0.12 long, 0.24 broad.

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

Definition.— (vel Dicyrtida multiradiata aperta) without thoracic ribs, with six terminal feet around the mouth. Cephalis free, with an apical horn.

The genus Anthocyrtoma and the four following genera form together the peculiar group of Carpocanida, comprising all those Sethophormida in which the original thoracic ribs are lost, and only the terminal feet remain. Anthocyrtoma is the simplest form of this group, possessing only six terminal feet, three primary perradial, and three alternating, secondary, interradial. It may be directly derived either from Lychnocanium, by interpolation of three interradial feet, or from Hexaspyris by loss of the sagittal ring.

1. Anthocyrtoma serrulata, Haeckel.

Anthocyrtis serrulata, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. vi. fig. 7.

Shell pear-shaped, rough, with obliterated collar stricture. Length of the two joints = 1 : 4, breadth = 1 : 3. Cephalis ovate, with very small pores, and a stout conical horn of the same length. Abdomen inflated, truncate, with larger, regular, circular pores, twice as broad as the constricted mouth. Six feet vertical, parallel, serrate, all of the same size, about as long as the cephalis.

Dimensions.—Cephalis 0.06 long, 0.05 broad; thorax 0.2 long, 0.17 broad.

Habitat.—Fossil in Barbados.

2. Anthocyrtoma alterna, n. sp.

Shell pear-shaped, smooth, with distinct collar stricture. Length of the two joints = 1 : 5, breadth = 1 : 6. Cephalis hemispherical, with a slender conical horn of twice the length. Abdomen inflated, subglobular, with regular, circular, hexagonally framed pores, three times as broad as the narrow, constricted mouth. Six feet conical, smooth, somewhat divergent, alternating, of different sizes; the three larger (perradial) half as long as the shell, and twice as long as the three smaller (interradial). (Similar to Anthocyrtis ventricosa.)

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

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