OF ARTS AND SCIENCES. 



233 



many of the spines, nearly equalling the radius of the test, had become 

 curved and assumed the characteristic appearance of Spatangoid spines. 

 Seen from below (Fig. 3), the large angular mouth, covered by a thick 

 membrane, was nearly central, somewhat anterior, the edge of the 

 mouth ou the level of the test, and a few small indistinct pores (Fig. 4) 



Fiff. 3. 



Fig. 4. 



arranged in parallel lines, showing the position of the future actinal 

 petal ; the ambulacral areas were occupied by coarse granulation, while 

 the tubercles of the interambulacral spaces were large with well- 

 developed crenulation, and already perforated. The interambulacral 

 areas were already broad, leaving but narrow ambulacral spaces, in 

 which the short, club-shaped ambulacral tubes could with difficulty be 

 traced ; they were largest 

 near the apex, and near the 

 actinostome (Figs. 4, 5). 

 Seen from above (Fig. 5), 

 the most marked feature 

 of all these young Echini 

 was the broad fasciole, oc- 

 cupying so large a part of 

 the abactinal surface, the 

 position of the interambu- 

 lacral area being clearly 

 marked by the two large 



tubercles at the extremity of these areas on the abactinal edge of the 

 fasciole. The whole fasciole was covered by a coarse granulation. 



Fig. 3. Young Hemicaster denuded of spines, seen from the actinal side. 



„ 4. Portion of actinal surface of Fig. 3, adjoining actinostome to show 

 structure of tubercles, a, ambulacral area with pores ; ia, ia, adjoin- 

 ing interambulacral spaces. 



„ 5. Fig. 3, seen from the abactinal side, somewhat more enlarged to show 

 the position of anal system (a), entirely enclosed by the peripetaluus 

 fasciole (/), the few ambulacral pores of tlie lateral ambulacra, anc' 

 the more numerous pores of the odd ambulacrum. 



