CALCAREOUS SPONGES. 735 



Genus 8. Pericharax Polejaeff [1883]. 



Diagnosis. Sponge colony individualised, with large central 

 cavity (probably a pseudogaster) opening by a wide vent 

 and surrounded by a very thick wall. Oanal system leuco- 

 noid, with sub-spherical, scattered, flagellate chambers, and 

 with subdermal cavities whose walls are supported by a 

 special skeleton derived partly from the inturned rays of 

 tangential dermal triradiates. Skeleton of the chamber 

 layer confused, composed of equiangular triradiates of two 

 very different sizes. 



For illustrations of this genus see Polejaeff [1883] and Dendy 

 [1913]. 



This genus was proposed by Polejaeff [1883] for a species, 

 Pericharax carteri, from Tristan da Cunha, but recent authors, 

 for the most part, have not accepted it. The discovery by the 

 ' Sealark ' Exj)edition of the original species, and of a new one 

 closely allied to it, has enabled us to make a careful study of 

 the question, and we are convinced that the genus is valid. 

 The position which we assign to it is justified, not only by the 

 character of the skeleton, but also, as in the case of Leucetta, by 

 the basal position of the nucleus of the collared cells in both 

 species. 



The dermal triradiates in both species are very curious spicviles, 

 with a strong tendency to irregular curvature of the rays, often 

 resulting in one or more of them dipping down deeply between 

 the subdei-mal cavities. 



Pericharax heteroraphis (Polejaeff 's P. carteri var. heterorwphis) 

 must be taken as the type of the genus. The same author's 

 P, carteri var. homoraphis, as we have noted above, appears to be 

 quite distinct, and is not a Pericharax at all, but probably a 

 Leucetta. Pericharax poUjaevi Breitfuss [1896 A], placed by its 

 author in this genus on account of the presence of subdermal 

 cavities, is really a typical Leucandra, for the presence of sub- 

 dermal cavities without a special supporting skeleton cannot be 

 regarded as of generic importance. Polejaeff also included in the 

 genus Haeckel's Leucandra citcumis, the position of which is 

 discussed by us under the genus Paraleucilla. 



We recognise the following as species of this genus : — 



1. Po heteroraphis Polejaeff. Type species of the genus. 



Pericharax carteri var. heteroraphis Polejaeff [1883]. 



2. P. peziza Bendy, 



Pericharax peziza Dendy [1913]. 



