GENEEA AKD GEOTJPS OE THE ECHENTOIDEA. 55 



IncertcB sedis. 



Genus Leptocidaris, Quenstedt, 1858, JDer Jura, pi. 90. fig. 10 ; 

 and 1874, Petr. Deutscl. p. 232, tab. 69. figs. 71. 



Test spheroidal; the ambulacra moderate and straight; the pores 

 are in arcs of triple pairs, and each compound plate is large, higher 

 than an interradial plate, and alternately broad and narrow ; small 

 perforated primary tubercles on alternate plates, or more distant. 



The ambulacral plates haye each a large adoral primary com- 

 ponent, which carries the tubercle and a middle and aboral demi- 

 plate. 



Interradial plates low and broad. 



Fossil. Jurassic : Europe. 



The description is taken from that mine of wealth, Quenstedt's 

 Petrefact. Deutschlands, Leipzig, 1874. The type is L. triceps, 

 Quenst. 



In the Eeport on the Echini of the ' Challenger' and ' Blake ' 

 Expeditions A. Agassiz described species of Aspidodiadema, a 

 genus which he defined comparatively rather than positively. He 

 gave his usual careful opinious regarding the affinities of the 

 genus, and noticed how it links together the Cidaridse and Dia- 

 dematidge. The descriptions of the species and the figures which 

 illustrate them are so clear and definite that all the taxonomic 

 difficulties surrounding them are really seized at a glance. A 

 palgeontologist would hardly hesitate to add Remicidaris to the 

 list of allied genera ; and any naturalist who has studied the 

 ancient and modern faunas would say that there is a wonderful 

 union of almost excessive modern characters, and others charac- 

 teristic of deep-sea dwellers, combined with the Hemicidaridean, 

 accompanied by a Cidaroid ambulacral structure. 



The paucity of interradial plates, each with a large perforate 

 and crenulate tubercle, associated with branchial peristomial in- 

 cisions, and with out imbricating ambulacral and interradial buccal 

 plates, there being only ten huge simple buccal plates, the am- 

 bulacral plates being lew simple primaries, with or without large 

 primary tubercles, may be said to be a jumble of characters which 

 will prevent the forms being classified with the families Hemici- 

 daridse and Diadematidse. It is proposed to form a family for 

 the genus. 



