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



The reader sees that there are many points in which I disagree with Dr. Marshall 

 Most of the contradictions are, however, insignificant, and the remaining ones, I feel 

 certain, are to be explained by the fact that Dr. Marshall's specimens were either in a 

 dried state or very badly preserved. At any rate, I see no reason against adopting both 

 the genus and the species. 



Colour. — Sandstone-yellowish. 



Habitat.— ^t&tion. 49, May 20, 1873, lat. 43° 3' N., long. 63° 39' W.; depth 85 

 fathoms ; gravel and stones. Ofi" Port Jackson, 7 fathoms. 



Psammopemma porosum, n. sp. 



In his paper on systematic rules Strickland suggests that generic and specific 

 designations should be given which allude to the main generic or specific character of the 

 given form ; — very good counsel indeed, yet it occurs but too often that whilst following 

 it the classifier creates very unfortunate systematic designations, and so far as the 

 species I am going to describe is concerned, I ieel by no means certain that — just as we 

 find AncorincB without any anchor-like spicules — specimens of Psammopemma porosum 

 will be found of no less density than that of the Challenger specimen of Psammopemma 

 densum from Port Jackson. Still I do not take refuge in naming the species in question 

 according to its second and undoubtedly more important character, for this latter character 

 may prove to be of a subgeneric consequence. The species is represented in the collection 

 by numerous small fragments, which, formless as they are, show distinctly that the 

 external shape of the specimen — or, perhaps, specimens — dredged by the Challenger must 

 have been of a rather stout, massive appearance. Apart from this character as well as 

 from the porosity, which latter peculiarity may stand in connection with the massive 

 shape of the animal, the fragments in question recall vividly as regards their form the 

 Challenger specimens of Psamviopemma densum, and especially that from Nova Scotia. 

 Their colour is a dirty sandstone greyish, and the presence in the parenchyma of foreign 

 enclosures (chiefly sand-grains, and, only in the upper skin, fragments of spicules) is well 

 marked in the roughness of the surfaces. 



As I remarked before, one of the characters of the species may be its porosity. I have 

 but to add that this peculiarity must be really regarded as characteristic at least of the 

 specimen, for there is no reason to suggest that the parenchymal cavities in question are 

 due to worms as in the specimens of Psammopemma densum examined by Dr. Marshall. 

 Except a Hydroid {Agl(eop>henia, sp. ?) rooting in one of the fragments and the doubtful 

 round bodies to which I shall refer later, I miss any parasitic inhabitants entirely. 



The second peculiarity characterising this form is the minuteness of its flagellated 

 cells, which are smaller than in any horny sponge hitherto described. It is only in some 

 Corticatte (StcUetta gruhei, Geodia gigas, Ancorina aaptos, Tethya lyiicurium) that I 



