378 DISCOVERY REPORTS 



are, indeed, similar in all respects but the possession of two sorts of anatriaenes by the 

 one species, and one sort by the second species. It seems unreasonable to doubt that the 

 two species are identical, but for this it must be presupposed that any category of 

 spicule is capable of differentiation into two sizes. A striking example of this is found in 

 Craniella disigma, Topsent (1904, p. 100), which differs from Tetilla cranium (Miiller) 

 Autt., in one respect only, that it has two sizes of sigmata instead of one. Here, again, 

 it seemed probable that Craniella disigma was identical with Tetilla cranium. To test 

 this I took a jar from the Porcupine collection, containing some thirty specimens 

 identified by Carter as Cranilla cranium (Miiller). Only one had been previously cut. 

 The specimens were all alike externally and proved, on being sectioned, to be all alike 

 internally; one of them, however, had two sizes of sigmata, exactly as in C disigma, 

 Topsent. Further, Clathria frondifera, var. dicliela, Hentschel (1912), is probably a 

 specimen of C. frondifera (Bowerbank) in which a similar differentiation has taken place. 

 Taking, now, all the variations to which the skeleton may be subject, it is not unreason- 

 able to suggest that the external form may conceivably offer a more reliable means of 

 identification, if only as the final arbiter. 



THE ABUNDANCE OF SPONGES IN THE ANTARCTIC 

 AND ITS GEOLOGICAL SIGNIFICANCE 



According to Prestwich {Geology: Chetnical, Physical and Stratigraphical, 1886, p. 125), 

 "in their geological relations the forms and distribution of the sponges are of the 

 highest interest". This being so it would be as well to be sure that the statements 

 upon which geological arguments are based are correct. Merely a superficial acquaint- 

 ance with geological literature is sufficient to show that this is not always the case. 

 There is, for example, a strong belief among geologists, as shown by the literature, 

 that the growth of sponges is most prolific in warm seas, and that, a priori, a deposit 

 rich in sponge remains must have been laid down in a warm sea. The abundance 

 of sponges in the Antarctic, as shown by the present collections, definitely proves 

 that in recent times at all events this is not the case. Judging by the collections and 

 by the verbal accounts of collectors, there is every reason to believe that sponges 

 are at least as abundant in the Antarctic as in, say, the West Indies, Australia or 

 the Indian Ocean. And the probability is that they are considerably more abundant. 

 Certainly, the average size of the specimens exceeds that observed in any other part of 

 the world. And finally, what is even more important from the geological point of view, 

 whereas a large percentage of the sponges in warmer seas are keratose or pseudo- 

 keratose, the remains of which are unlikely to be preserved in a fossil state, those of 

 the colder waters are almost exclusively siliceous, and the spongin, when present, does 

 not form so great a percentage of the skeleton as in corresponding species in the warmer 

 seas. 



There is, further, the belief that sponges reached their "maximum development in 



