Plate XXI. 



Urechinus Naresianus Al. Ag. 



P. 90. 



Fig. 239. The .?kel'etoii of Urechinus Naresianus Al. Ag., laid out. 



Fig. 240. The buccal membrane of the same. 



Fig. 241. The anal membrane of the same. 



Fig. 242. The calycinal system of the same. 



