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



Genus 346. Porocapsa^ u. gen. 



Definition. — S p h se r o c a p s i d a witli twenty radial spines shorter than the radius 

 of the shell ; therefore their distal ends not connected with the twenty perspinal holes, 

 which are simple, not prolonged into radial tubes. 



The genus Porocapsa and the following Cannocapsa form together the small sub- 

 family of Porocapsida, distinguished by the peculiar reduction or retrograde development 

 of the twenty radial spines ; aU these twenty are present and disposed according to the 

 Miillerian law of the Icosacantha, but they are shorter than the radius of the shell and 

 therefore do not reach it. In the ideal prolongation of the spines the shell is pierced 

 by twenty simple quadrangular or circular perspinal holes. 



1. Porocapsa murrayana, n. sp.* (PL 133, fig. 7). 



Perspinal holes cruciform, with smooth thickened margin or with foiu' short teeth between the 

 four lobes. Porules of tlie shell simple, without ring and dimple. Four edges of the spines 

 smooth. (Differs from jSpJuxrocapsa criiciata, PI. 135, figs. 6, 7, living in the same locality, mainly 

 in tlie reduction of the radial spines, which do not reach the shell.) 



Dimensions. — Diameter of the shell 0'28 ; length of the spines 0"2. 



Habitat. — North Atlantic, Fseroe Channel, Gulf Stream (expedition of H.M.S " Triton," August 

 1882), John Murray, surface and in depths from 40 to 640 fathoms. 



2. Porocap>sa tetrodon, n. sp. 



Perspinal holes cruciform, with four triangular prominent teeth between the four lobes of the 

 cross. Porules of the sheU with an elevated polygonal ring, in the bottom of a dimple. Four edges 

 of the spines elegantly denticulate. 



Dimensions. — Diameter of the shell 0'36 ; length of the spines 0'12. 



Habitat. — North Pacific, Station 253, surface. 



3. Porocapsa octodon, n. sp. 



Perspinal holes square, with four larger prominent teeth on the sides of the square, and four 

 smaller teeth on its comers. Porules of the sheU surrounded by an elevated ring with elegantly 

 crenated irregular margin. Four edges of the spines smooth. 



Dhnensions.—Ttiwaei&v of the shell 0'48 ; length of the spines O'lS. 



Habitat. — Arctic Ocean (Greenland), in the contents of the stomach of the Peromedusa, 

 Periphylla hyacinthina. 



' Porocapsa = Porous capsule ; ■tto^o;, xki^k. 



