Page:Scientific results HMS Challenger vol 18 part 2.djvu/385

Rh 1. Spongopyramis spongiosa, n. sp. (Pl. 56, fig. 10).

Plectopyramis spongiosa, Haeckel, 1881, Prodromus et Atlas, ''loc. cit.''

Shell partly or entirely enveloped by spongy framework, slender, pyramidal, with rather straight outlines. Cephalis very small, ovate, hyaline. Thorax with nine very stout and nearly straight ribs, which are connected by fifteen to twenty or more irregular, interrupted transverse bars. The irregular quadrangular meshes so produced are filled up by an irregular secondary network, with meshes of very different size and form. The dense spongy envelope, which in the specimen figured covered only half the shell, was complete in another older specimen.

Dimensions.—Cephalis 0.015 long, 0.01 broad; thorax 0.4 long, 0.25 broad.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

2. Spongopyramis spongoplecta, n. sp.

Shell entirely enveloped by spongy framework, pyramidal, with straight outlines. Cephalis ovate (twice as large as in the preceding species), with small circular pores. Thorax with twelve stout and straight ribs, which are connected by twenty to twenty-five annular, transverse bars. The subregular square meshes so produced are filled up by irregular, spongy network, which envelops the whole shell more loosely than in Spongopyramis spongiosa.

Dimensions.—Cephalis 0.03 long, 0.02 broad; thorax 0.5 long, 0.2 broad.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

Definition.— (vel Dicyrtida multiradiata aperta) with numerous radial ribs in the wall of the pyramidal thorax, prolonged into divergent terminal feet. Network simple. Cephalis commonly with several horns.

The genus Acanthocorys and the following nearly allied Arachnocorys possess a near relation to the three preceding pyramidal genera, but differ from them in the terminal prolongation of the radial ribs, which are commonly spiny and form a corona of free feet around the mouth of the thorax. The cephalis is usually much larger than in the three preceding genera, and bears a variable number of radial horns. Therefore these two genera are probably older and nearer to the common ancestral form of the Sethophormida than the preceding genera. It may be derived directly from Dictyophimus by interpolation of three secondary (interradial) ribs between the three primary (perradial) ribs.