Page:Scientific results HMS Challenger vol 18 part 2.djvu/643

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Definition.— (vel Stichocyrtida eradiata clausa) with an apical horn on the cephalis, and a basal terminal spine on the last joint.

The genus Artocapsa differs from Cyrtocapsa, its ancestral form, by the development of a vertical terminal spine, or a bunch of spines, on the base of the last joint, and bears therefore to it the same relation as Rhopalatractus does to Rhopalocanium.

1. Artocapsa fusiformis, n. sp. (Pl. 76, fig. 5).

Shell spindle-shaped, rough, with five slight strictures, decreasing uniformly from the broader middle towards both poles, with a strong, pyramidal, terminal spine at each pole. Length of the six joints = 2 : 5 : 3 : 3 : 2 : 5. Cephalis hemispherical, hyaline, without pores, its horn half as large as the basal spine. Pores small and numerous, subregular, circular.

Dimensions.—Length of the shell (with six joints) 0.2, breadth 0.09. Length of the single joints, a 0.02, b 0.05, c 0.03, d 0.03, e 0.02, f 0.05.

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

2. Artocapsa spinosa, n. sp. (Pl. 76, fig. 10).

Shell spindle-shaped, spiny, with five distinct strictures. Length of the six joints = 2 : 3 : 2 : 5 : 4 : 4. The fourth joint is the broadest, and much larger than the five other joints. The first and the last joints are similar in size and form, hemispherical, armed with some larger, irregular, conical spines. Pores irregular, roundish, of variable sizes.

Dimensions.—Length of the shell (with six joints) 0.2, breadth 0.09. Length of the single joints, a 0.02, b 0.03, c 0.02, d 0.05, e 0.04, f 0.04.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

3. Artocapsa infraculeata, Haeckel.

Eucyrtidium infraculeatum, Stöhr, 1880, Palæontogr., vol. xxvi. p. 106, Taf. iv. fig. 13.

Shell subcylindrical, rough, with five annular septa. Length of the six joints = 2 : 3 : 4 : 4 : 4 : 3. The third, fourth, and fifth joints are nearly equal in length and breadth, whilst the second and sixth are cupola-shaped. The cephalis is very small, subspherical (regarded by Stöhr as a "large pore"), and bears a short conical horn. The last joint bears a bunch of basal spines.

Dimensions.—Length of the shell (with six joints) 0.2, breadth 0.09. Length of the cephalis 0.02, second and sixth joints 0.03, third, fourth, and fifth joints 0.04.

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