E. IMPERIALIS. — SPICULATION. 73 



surface in coherent bundles, wliicli stand each in association with 

 the distal ray of certain especially strongly developed dermal 

 hexactins presently to be noticed. The bundles constitute the 

 bristle-like prostalia already described. Just the same kind of 

 prostalia is known to occur also in some other species ; e.g., in 

 E. marshal! i Ij., JE. nodosa F. E. Sch. 



The osoularia (fig. 17) are mostly thick-rayed, plump- 

 looking hexactins and pentactins. Both these forms occur in 

 about the same numerical proportion. In addition to them, there 

 also occur not uncommonly forms which nearly approach or 

 virtually are stauractins or compass- needle-like diactins. Their 

 size is exceedingly variable, those near the edge of the oscular 

 membrane being much smaller than others situated in more 

 peripheral positions in the zone. The former may measure only 

 120/^ in axial length and lb !> in breadth of the rays, while 

 some of the latter may attain 4öO /^ and 50/^ in the corresponding 

 dimensions. The rays are either rounded at the end or pointed 

 and conical in shape. The spicules lie thickly crowded for the 

 most part in several layers and apparently without regularity as 

 to the disposition of the axes in relation to the surface of the 

 zone. In the case of oscula of comparatively recent formation, 

 the oscularia are always much less numerous than in those of 

 long s'tanding. Noteworthy is the fact that there exist in the 

 immediate neighborhood of the zone certain hexactins and pen- 

 tactins, which, considered in respect of position, size and general 

 appearance, might well be considered as standing intermediately 

 between the oscularia on the one hand and the hexactin-paren- 

 chymalia and the pentactin-gastralia on the other. 



