REPORT ON THE RADIOLARIA. 1297 



25. Sethoconus venosus, n. sp. (PL 55, fig. 2). 



Pldeliaracliniiim venosum, Haeckel, 1881, Prodromus, p. 430, et Atlas, loc. cif. 



Cephalis subspherical, with a stout prismatic horn twice the length, bearing three denticu- 

 late edges. The uppermost part of the thorax is supported by three diverging, radial beams 

 arising from the deep collar stricture. Thorax wide, conical, nearly twice as long as broad, with 

 slightly convex, thorny outlines ; its delicate network is composed of very irregular, polygonal 

 meshes of different sizes, separated by stronger bars, and of numerous very small polygonal pores 

 separated by very thin bars inside the former. The central capsule of the figured specimen 

 exhibited in the upper third of the thorax four large club-shaped lobes, which arose from a very 

 small sphere enclosed in the cephalis and containing the nucleus. 



Dimensions. Cephalis 0'02 long, 0'03 broad ; thorax 0'4 long, 0'3 broad. 



Habitat. Central Pacific, Station 271, surface. 



Genus 573. Periarachnium, 1 Haeckel, 1881, Prodromus, p. 430. 



Definition. -S ethocorida (vel Dicyrtida eradiata aperta) with conical or cam- 

 panulate, gradually dilated thorax, and widely open mouth. Primary lattice - shell 

 enveloped by an external arachnoidal mantle. Cephalis with one or more horns. 



The genus Periarachnium has been derived from those forms of the preceding 

 Sethoconus, in which the conical thorax is covered with simple spines (Phlebarachnium) 

 or branched spines (Cladarachnium). By communication of the branches of these 

 spines a second outer shell is formed, which, like an arachnoidal mantle, envelops the 

 inner primary shell. 



1. Periarachnium periplectum, n. sp. (PL 55, fig. 11). 



Cephalis hemispherical, separated from the thorax by a sharp collar stricture, from which 

 arise three internal, diverging beams supporting its upper third. Thorax campanulate, conical, 

 about as long as broad, with slightly convex outlines. The delicate lattice-work of the entire shell 

 is double ; the inner composed of subregular, hexagonal meshes ; the outer of larger, irregular, 

 polygonal meshes. The bars of the inner are much thicker than the thin threads of the outer. 

 Both shells are connected by numerous bristle-shaped beams. The central capsule of the figured 

 specimen exhibited in the upper part of the thorax three club-shaped lobes, which arose from 

 a sphere enclosed in the cephalis and containing the nucleus. 



Dimensions. Cephalis 0'02 long, 0'03 broad ; thorax 0'15 long, 012 broad. 



Habitat. Central Pacific, Station 271, surface. 



1 Periarachniurn = Shell enveloped by cobweb; {/, dactjcainy. 

 (ZOOL. CHALL. EXF. PART XL. 1886.) Rr 163 



