Pw OKIXOSEANA. — YOUNG SPECIMENS. 243 



ray of which is rough-surfaced and rounded at the end. The 

 diactin-parenchymalia and spinose microxyhexactins are present 

 in greater abundance than before. Besides graphiocomes, there 

 are now to be seen floricomes, oxyhexasters and oxystaurasters, 

 though as yet in quite limited numbers. 



In short the small specimen in question may be said to bear 

 the essential characteristics of the adult It. okinoseana, except in 

 the important respects that the terminal osculum is simple instead 

 of being covered by a sieve-plate, and that the dermalia are 

 predominantly peutactins. 



3. By the side of the above specimen and on the same dead 

 skeleton, was found another young specimen, which, though 

 broken off in the upper part, must have had a somewhat larger 

 body. A few parietal oscula open in the portion of the sponge-wall 

 still remaining. As to the spiculation, the one important point 

 in which this differs from the last specimen consists in the fact 

 thiit the hexactin-dermalia are present in a notably increased 

 number, — in about the same numerical proportion as the pentactiu- 

 dermalia (PI. A"II, fig. 12). The hexactin-dermalia compare well 

 with those of old specimens of R. okinoseana. I have noticed 

 that the pentactins have on an average stronger ra)^s than the 

 hexactins and that the latter are very variable in size, the 

 smallest having very slender rays indicative of its comparatively 

 recent origin. Further, I may say that the paratangentials of 

 the pentactins generally, though not always, overlie those of the 

 hexactins. The evidences are in favor of the conclusion that, 

 whereas the first formed dermalia are pentactins, those which 

 be"-in to develop later are all hexactins, and that these are, as 



& -1- 



a general rule, added to the dermal layer from below. 



