35 



represent the young stage. Should subsequent observations show that they do 

 belong to another species, their present name, having served its purpose, can 

 be dropped. The thi'ee specimens represented in fig. 23-25, plate II, show that 

 the shape is, for a certain extent, subject to variations ; they all however re- 

 semble a pear, or an egg pointed below. The smallest of the four specimens in 

 the " Investigator " collection (pi. II, f. 25) is more truncate above than the others 

 and destitute of an oscule. The others* possess a more or less circular oscule, 

 which increases in width with the size of the sponge to a diameter of 3 mm. It is 

 not covered by a sieve, and has a sharp margin which, in the largest specimen 

 (pi. II, f. 23) is already slightly elevated. On the outer surface the quadratic 

 dermal reticulation is, particularly in the larger specimens, clearly discernable. 

 Looking through the oscule into the gastral cavity, one notices a central cone 

 extending upwards to the level of the oscule and connected with the body-wall 

 by three or four unequally developed radial septa, which terminate above with 

 concave margins. Greater or smaller parts of the root-tuft are still attached 

 to the specimens. These root-tufts are slender and composed of not more than 

 10-50 spicules. Only in the largest specimen, represented in fig. 23 on plate 

 II, an indication of a Palythoa crust, in the shape of a single contracted spheri- 

 cal polyp attached to one side of the root-tuft, just below the body of the 

 sponge, is seen. 



In shape, size and position the macroscleres do not differ essentially from 

 those of Hyalonema indicum; the microscleres show however some peculiarities. 

 The dermal pinules are in Hyalonema indiaim 300-600 a* long, in H. pirum. on 

 an average only 300 h- long. Their thickness is about the same, their spines are 

 less numerous in the latter. 



The dermal macramphidiscs are rather variable. In shape, size and abun- 

 dance they agree with those of Hyalonema indicum. The mesamphidiscs on the 

 other hand, although resembling in shape and size those of Hyalonema indicum, 

 are here not nearly so plentiful. In the micramphidiscs, which are not parti- 

 cularly frequent, no essential difference is discernable. 



The same applies to the equally-abundant, rough parenchymal micro-oxyhex- 

 actines (pi. II, f. 27). 



The plane oxytetractines of the sub-species of Hyalonema indicum are 

 entirely absent. 



The largest of the specimens, which i§ 20 mm. long and 12 mm. thick, was 

 found in the Andamans, near Ross Island, in a depth of 485 m.=265 fths. 

 The three other, considerably smaller specimens, two of which are figured in 

 figs. 24 and 25 on plate II, were found in the Andamans, in the vicinity of North 

 Sentinel Island, also in a depth of 485 m.=265 fths. 



