ON THE YOUNG STAGES OF ECHINI. 743 



ovoid. At the same time the miliary tubercles increase rapidly in number, 

 forming clusters of small tubercles, embossing the plates of both areas. The 

 anal system is covered by three large triangular plates {PL XVI f. 5, 14), the 

 anus opening near the edge of the system, in a narrow slit covered by very 

 minute plates. The mouth, as the young increase in size, becomes more and 

 more sunken {PI. XVI. f. 9, 18, 20). The buccal membrane is covered with 

 minute plates {PL XVI f. 9), the mouth opening in the centre. There are 

 as yet no signs of phyllodes or of bourrelets, which appear only later, the 

 bourrelets being at first accumulations of small tubercles between the phyl- 

 lodes {PL XVI f. 20). When measuring about half an inch in length, the 

 young Echinolampas resembles Caratomus to such an extent {PI. XVI 

 f. 8- 10) that this stage was considered for a time a living representative of 

 Caratomus. The larger series collected by Mr. Pourtales in his second ex- 

 pedition showed conclusively the relationship to Echinolampas, and proves 

 the correctness of the step taken by Desor in removing Caratomus and allied 

 genera from the Galeritidae, and placing them among the Cassidulidae. on 

 account of the semipetaloid nature of the apical portion of the ambulacra. 



Among Spatangoids proper, the examination of young specimens shows 

 that they undergo great changes in outline during their growth; that the 

 posterior part of the test is especially subject to variation ; that the position 

 of the anus is exceedingly variable in one and the same species ; that the 

 mouth is not labiate in the young as in the adult; that the peripetalous 

 and lateral fascioles do not greatly change their limits, but that the subanal 

 and anal fascioles are subject to extreme modifications during their growth, 

 and cannot be used as distinctive features of generic value, while the per- 

 manence of the peripetalous and lateral fascioles is of great systematic value. 

 The ambulacra] petaloids also are greatly modified with age, generally becom- 

 ing confluent, while in the young they are remarkably distinct and the pores 

 not conjugated. The Cassiduloid-shaped mouth of young Spatangoids {PL 

 XVII f. 13, 16; PL XIX. f. 1.3), as well as the existence of several Spatangoids. 

 both fossil and recent, in which the mouth has a similar structure, is as con- 

 vincing a proof as necessary of the correctness of uniting Cassiduloids and 

 Spatangoids in the same suborder. 



Young Brissopsis lyrifera, less than a quarter of an inch in length, are 

 cylindrical {PL XIX. f. 1-8), the mouth having a Hat, crescent-shaped edge, 

 the test is truncated vertically at the posterior edge, surrounded by a promi- 

 nent elliptical subanal fasciole; the peripetalous fasciole is elliptical, undulat- 



