80 I. IJIMA : HEX ACTIN ELLIDA. I. 



ridges, which, in such young specimens much more frequently 

 than in the older ones, are fringed with an irregular row of 

 bristle-like prostalia. Fig. 3, PL I, may be taken as an illustra- 

 tion of the general appearance of the sponge at the stage in 

 question. The parietal prominences are best developed on the 

 middle of the body but are yet quite undeveloped close to the 

 sieve-plate end. They are nowhere so conspicuous as in old 

 specimens, but when compared with E. marshalli of about the 

 same size, they give a jagged appearance to the sponge surface 

 sufficient to serve as a distinguishing feature. 



Secondly, the size of the floricome presents a certain con- 

 stant difference in the two species. It seems that in all Euplectella 

 species the said rosette is on an average somewhat smaller in 

 young than in old specimens. Now, whereas in old E. marshalli 

 it never exceeds 80 /-« in diameter, all the small E. imjyerialis 

 under consideration have it appreciably larger ; here the diameter 

 may reach 91 /^ or over, although some other floricomes in the 

 same individual may run down to 84 // in diameter. 



Further there are some other points w^iicli at times may 

 serve as an aid in referring young specimens to one or the other 

 of the species in question. 1) The locality and depth from which 

 the specimens were obtained ; for, so far as my knowledge goes, 

 tlie two species seem to have each its own sphere of distribution 

 both horizontally and vertically (see p. 60). 2) The character 

 of the substratum as exemplified by the matter contained in the 

 root-tuft; for, while E. imperialis exclusively inhabits sandy or 

 muddy bottoms, the other species is apparently confined to 

 the coarser shelly grounds. 3) Tlie species of the Crustacean 

 immate (see anon, under Miscellaneous Notes). Constant as the 

 difference in this regard seems to be, the drawback is that in 



