SEA-URCniNS. 



493 



shfipe when the height of tlie test diminished. The ambulacra 

 in all (Jlypeastroids "are either petaloid or subpetaloid, but Cono- 

 ch/pens, from the Upper Cretaceous, serves to link the simple 



Text-fiir. GO. 



Phvlo<^eiietic talilo of tlie Holectypoida and tlieir allies. Names of Holcctypnid 

 ' Vi'wa are connected by thick lines, those of other orders by thni lines. JNo 

 details are inserted in p-oups other than the Holectypoida, the names in tlie 

 external groups beins: those of the earliest-known genus that has been 

 Ratisfactorily described. Short, thick, horizontal lines above names indicate 

 that the genera became extinct at that horizon, and left no direct descendants. 



ambulacral pores of Discoklea with the more elaborate structures 

 of the later genera. Perhaps, if the jaw-structures of Cono- 

 clypeus were to be discovered in a more perfect condition than 



