RHABDOCALYPTÜS MOLLIS. 267 



fore disposed to consider them as of inconstant occurrence in the 

 species. Possibly they are produced only under certain abnormal 

 conditions. 



The discodasters (PL XX.,. fig. 5) are found scattered in 

 the wall, but in especial abundance in the subdermal space as 

 was noted by F. E. Schulze. I may here note that contrari- 

 wise in R. capillaius the same spicule is most numerous in the 

 subgastral region. What causes such a dissimilar distribution 

 can certainly not be told. In diameter the spicules in question 

 vary from 130,« to 175 /j- (on an average 140/^-). They are nearly 

 as large as, or but slightly larger than, the average oxyhexasters 

 of the species. The central node exhibits the six hillock-like 

 prominences more or less distinctly. The principals (secondary) 

 take up about one-third or less of the entire ray-length ; they 

 are 5 n or more thick iu the middle. Number of terminals in a 

 tuft, 5-9 ; rarely as few as 3 or even 2. The tuft is gently 

 expanded distally, the terminals composing it being each slightly 

 bent outwards or, as is sometimes the case, nearly straight. The 

 surface of terminals is slightly rough ; under the immersion system 

 the roughness may be seen to be caused by reverted microtubercles. 

 The terminal discs are either simply pinhead-like or show seven 

 or eight marginal teeth, the latter being the case in the larger 

 discoctasters. 



Not infrequently are the discoctasters malformed in that some 

 terminals remain free without being incorporated into any of the 

 secondary principals. Noteworthy seem the few instances that 

 came under my observation, in which the terminals stood out in 

 eight tufts directly from the tubercled central node, without 

 coming into fusion in the basal parts. 



