Page:Scientific results HMS Challenger vol 18 part 1.djvu/1064

856 2. Octopelta furcella, n. sp.

Apophyses of the eight tropical spines forked, each with two parallel simple fork-branches, about as long as their distance from the outer shell. On the base of each spine (in the outer shell) two kidney-shaped aspinal pores, about twice as broad as the other irregular pores.

Dimensions.—Diameter of the outer shell 0.1, of the inner 0.04.

Habitat.—South Atlantic (off Tristan d'Acunha), Station 332, surface.

3. Octopelta scutella, n. sp. (Pl. 133, fig. 5).

Apophyses of the eight tropical spines crossed by a transverse beam, which is again crossed by two perpendicular branches; by union of these branches each tropical spine forms a square shield with four crossed pores and twelve to sixteen marginal spikes. On the base of each spine (in the surface of the outer shell) four crossed aspinal pores which correspond to those of the free shields; these are somewhat larger than the other pores.

Dimensions.—Diameter of the outer shell 0.12, of the inner 0.06.

Habitat.—Tropical Atlantic, Station 348, surface.

Definition.— with eight simple spines (four equatorial and four hydrotomical polar spines) and with twelve spines protected by external free apophyses (eight tropical and four geotomical polar spines).

The genus Dorypelta, the most common of all Phractopeltida which are protected by free apophyses, exhibits a very peculiar differentiation of its twenty radial spines. There are constantly eight simple spines and twelve spines with apophyses. The eight simple spines are the four equatorial spines and four polar spines placed in the hydrotomical median plane. The four other polar spines (placed in the geotomical meridian plane) and the eight tropical spines are protected by two opposite apophyses, which are now simple, now branched or shield-shaped. A similar differentiation occurs in no other Acanthophractida.

Definition.—Free apophyses of the radial spines simple, not branched.