24 THE VOYAGE OE H.M.S. CHALLENGER. 



species. In ChcBtoderma nitidulum, Loveu, the calcareous needles, for instance, on the 

 hind end of the body are, according to Greeff's rejDort (Anatomie des ChiBtoderma 

 nitidulum, Lovdn, Zeitschr. f. wiss. Zool., Bd. xxvi. Taf. xiii. figs. 24-26), also flattened, 

 but they are not elliptical in cross-section, like those of Chcetoderma militare. And 

 again, the spicules on the body of the latter are much less numerous, and we cannot doubt 

 that the examination of fresh or well-preserved specimens of the tropical form would 

 reveal other difi"erenccs, which, with the material before me, I am unable to detect. 



