Page:Scientific results HMS Challenger vol 18 part 2.djvu/445

Rh 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.— (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.