MEM. M. C. Z., IX. No. 2. — ECHINODEEMATA. 33 



43. Young StrongyTo-.entrotus, measuring one fifteenth of an inch in diameter, including the siiines ; a number 



of long-stemmed pedieellari;e have developed on the abactinal side ; the tentacles have become quite 

 slender, and carry a comparatively large sucking disk ; the spines have lost their embryonic character, and 

 have assumed the general appearance of those of the adult. The anal system is very prominent, a large 

 circular opening covered by a single plate, a, leaving the anal opening on one edge of the anal system. 



44. The test of a young Sea-urchin, in the stage of tigs. 41, 42, stripped of its spines, seen from the actinal side ; 



the actinal system is comparatively large, and, as in C'idaris, the tubercles are large and few in number ; no 

 miliary tubercules are as yet formed. The teeth are simple, and the accessory parts of the jaws are not 

 developed. 



