830 THE VOYAGE OF H.M.S. CHALLENGER. 



on the base, with two divergent straiglit branches (similar to those of Rystricliaspis furcata, PI. 138, 

 fig. 9). Eadial main spines two-edged, sword-Hke, nearly as long as the diameter of the shell. 



Dimensions. — ^Diameter of the shell 013, of the pores O'OOS. 



Habitat. — Central Pacific, Station 272, surface. 



4. Acontaspis capillata, n. sp. 



Shell very dark and thick walled, non-transparent, with very numerous (three hundred to four 

 hundred or more ?) deep funnel-shaped dimples, each of which is perforated by a smaR circular pore 

 (forty aspinal, two hundred to three hundred coronal, and fifty to one hundred sutural pores ?). The 

 high crests between the dimples bear very numerous simple by-spiues, nearly half as long as the 

 radius, so that the shell appears covered with haii's. Piadial main spines very long and thin, 

 cylindrical, longer than the diameter of the shell. 



Dimensions. — Diameter of the shell 0'2, of the pores 0'012. 



Salitat. — Xorth Pacific, Station 244, surface. 



Subfamily 2. Tessaraspida, Haeckel. 



Definition. — D o r a t a s p i d a with twenty radial spines, eaeli of wliich bears four 

 ■crossed apophyses (opposite in pairs). The spherical shell is composed either of the 

 meeting branches of these apophyses (Stauraspida), or of twenty perforated plates, 

 produced by concrescence of their branches (Lychuaspida). 



A. Tribe II. Stauraspida, Haeckel, 1881, Prodromus, p. 467. 



Definition. — D o r a t a s p i d a with spherical shell, which is composed either of 

 the meeting branches of the four crossed apophyses only, or exhibits four to twelve 

 perforated plates which are produced by the crossed apophyses of four to twelve radial 

 spines (but never of all twenty spines). Each plate bears four crossed pores. 



Genus 358. Stauraspis,^ Haeckel, 1881, Prodromus, p. 467. 



Definition. — Dorataspida without perforated plates; shell composed only of 

 the meeting branches of the four crossed apophyses, which arise (opposite in pairs) 

 from each radial spine. Condyles of the branch-ends without by-sj)ines. 



The genus Stauraspis is the most simple and primitive form among all Tessara- 

 spida, or that subfamily of Dorataspida, in which the shell is composed of twenty 



' StaMras2'is = Cross-sliield ; hthv^os, aaTtf. 



