204 BULLETIN OF THE 



s ime of the genera of this collection (Podocidaris), there can now be 

 uo doubt that pedicellariae are nothing but modified spines; (he exist- 

 ence of pedicellariae surmounting a tubercle and moved by the same 

 mechanism as spines, as well as the mode of formation of the pedicel- 

 lariae, as observed in Asteracantbion and Spatangoids, by Miiller and 

 myself, proves conclusively that they are only more sensitive spines, 

 performing the functions of scavengers or of providers, according to 

 their position. 



The Cassiduloid-shaped mouth of young Spatangoids, as well as the 

 existence of several Spatangoids, both fossil and recent, in which the 

 mouth has a similar structure, is as convincing a proof as necessary of 

 the correctness of uniting Cassiduloids and Spatangoids in the same sub- 

 order, though the name given by Albin Gras, of " Irregular," is hardly 

 what could be desired. 



Young Bris-opsis lyrifera, less than a quarter of an inch in length, are 

 cylindrical, the mouth having a flat, crescent-shaped edge, the test trun- 

 cated vertically at the posterior edge, surrounded by a prominent ellip- 

 tical sub-anal fasciole ; the peripetalous fasciole is elliptical, undulating; 

 the anus is placed near the posterior extremity of the fasciole. The odd 

 ambulacrum carries four or five large tentacles with lobed disk; the pores 

 of the odd ambulacrum are single, not in pairs ; the other ambulacra are 

 short, straight, well defined, consisting of three and four pairs of pores 

 not yet conjugated. In older specimens the posterior edge of the mouth 

 becomes labiate, the anus approaches the subanal fasciole, which sends 

 out a rudimentary anal branch, eventually uniting with the peripetalous 

 fasciole, the outline of which becomes more pentagonal, undulating, 

 and elongated with the increasing size of the petaloid ambulacra. The 

 posterior edge becomes more bevelled witli age, the subanal plastron 

 more prominent, tin- lateral pairs of ambulacra gradually tend to unite, 

 passing from a strictly Brissopsis outline to one considered hitherto 

 characteristic of Toxobrissus. The spines ; n all young Spatangoids are 

 strikingly larger in proportion to their size than in the adult. 



In Echinocardium cordatum the changes of the mouth, of the out- 

 line of the internal ainbulacral fa-eiolc, and the gradual confluence of 

 the lateral ambulacra are similar to those of Brissopsis; the posterior 

 extremity undergoes the greatesl change in outline; the subanal plas- 

 tron h very prominent; in fact, the outline of young E. cordatum recalls 

 K. jibbosum. The subanal fasciole and anal branch are at first united, 



