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



together by a scarce maltha. The porous surface bears conical elevations, and on the 

 top of each cone opens a large osculum. 



Holopsamma argillaccum is represented in the Challenger collection by a single 

 small specimen, in the form of an irregular, roundish, tuberose lump, the diameter of 

 which is between 12 and 22 mm. The dry sponge is like a piece of red clay, quite 

 hard and solid, of a reddish grey or light red colour, but it is porous, and transverse 

 sections show the branched canals, proving its sponge-nature (fig. 6B). The smallest 

 inhalent canals open everywhere on the surface by the usual dermal pores ; the larger 

 confluent canals open into a few main branches, and each of these opens on the top of 

 a conical protuberance by a large osculum (fig. 6B, o). Attempting to isolate the 

 canals from the massive pseudo-skeleton, I was able to discover a few roundish sacs in 

 the course of the smaller canals, apparently the remnants of flagellated chambers. 

 A closer examination of the canal-system, however, was not possible. The fine 

 argillaceous matter, which forms the main-mass of the sponge, is composed of the 

 numerous mineral particles characteristic of the red clay, such as would be produced 

 by the decomposition of felspathic minerals, pumice, and other volcanic products ; 

 intermingled are siliceous spicules of different sponges, and their fragments ; all these 

 xenophya are cemented together by a small quantity of clear maltha. No Spongo- 

 xenise were found in this species. 



Genus 6. Psammopemma? Marshall (1880). 



Definition. — Psamminidae with an irregular massive or lumpy body, the surface of 

 which is pierced everywhere by small dermal pores, but showing no larger openings or 

 oscula. 



The genus Psammopemma was founded by Marshall in 1880 upon some Australian 

 sponges preserved in the Museum of Jena. He characterised it by the complete absence 

 of spongin-fibres, the crusty, lumpy, or cake-shaped body being supported by sand or 

 other foreign bodies, connected only by a small quantity of protoplasm. The sandy 

 body is traversed by very narrow branched canals, which exhibit no distinct oscula or 

 larger exhalent openings. This latter character mainly distinguishes Psammopemma 

 from Psammina and from Holopsamma ; both these genera possess distinct oscula, as the 

 opening of wide exhalent main canals. The two species of Psammopemma, which 

 Polejaeff describes in his Report on the Keratosa, 2 and which were collected by the 

 Challenger in shallow water, seem to belong to Cerelasma (cf. below). The author 

 says that " the secretion of the horny substance has been reduced to the formation of 



1 Psammopemma = Sandy cake, ■d/a/y.y.a, Triy-i/.a. 

 - inc. cit., p. 45. 



