GEISTEUA AND aEOUPS OF THE ECHIISTOTDEA. 249 



A subanal fascicle, concave towards the distant periproct, with 

 or without anal branches ; a peripetalous fascicle well developed, 

 more or less flexuous. Plates of the membranes of the peristome 

 and periproct largest at the edges and smaller near the orifices. 



Fossil. Eocene : England, Europe, Asia, Java. Miocene : 

 Europe, N. America, W. Indies. Pliocene: England, Europe. 



Mecent. North Atlantic, Norwegian and British seas, Medi- 

 terranean, Florida Gulf-stream, Sombrero, Caribbean Islands, 

 Formosa, Siam, East Indies, New Caledonia, Luzon, Tahiti, New 

 Zealand. Range from 1100 to 2435 fms. 



The curving of the paired ambulacra is well seen in the Sindian 

 species, and it is evident that such a character is not sufficient to 

 separate a new genus ; moreover the continuation of the rows of 

 pairs of pores so as to form a curve across the postero-lateral in- 

 terradia is subject to great variation. The general shape of indi- 

 viduals of the same species is remarkable and has necessitated 

 the introduction of an alteration in the definition of the genus ; 

 this is the result of A. Agassiz's examination of the Echini of the 

 ' Blake ' dredging-expedition. 



M. Cotteau defined a genus Cyclaster in 1856, and Desor 

 placed it as a synonym of JBrissojJsis in his ' Synopsis,' 1858. In 

 1863 M. Cotteau reasserted the right of Cyclaster to a generic 

 position, and wrote that Brissopsis differed because it had an 

 anterior groove and very slightly divergent and atrophied paired 

 ambulacra. Dames described and drew two species of Cyclaster 

 in ' Palseontographica,' 1877, Bd. xxv. ; and his figures and de- 

 scriptions agree with M. Cotteau's ideas ; but there is no vestige 

 of a peripetalous fascicle, and there are four closely-placed 

 genital pores. It is possible that the fascicle may have been 

 worn off; nevertheless the ornamentation of the test is given 

 without any evidence of it. Since that time several species have 

 been removed from Cyclaster by M. Cotteau, and a fresh generic 

 character has been added by him to which exception must be taken. 



The characters relied upon are the absence of an anterior am- 

 bital groove, the divergent antero-lateral ambulacra, a peripetalous 

 fascicle which is somewbat angular, a subanal fascicle, and the 

 presence of only three genital pores, that of the right anterior 

 basal plate being absent ; the extension of the madreporite cen- 

 trally, with separation of the posterior basal plates. In 1887, 



