46 IMr. F. A. Batlier on Eocidaiis and 



the rules of nomenclature, without regard to ulterior conse- 

 quences, seemed to have reduced Eocidaris to two species so 

 obscure that no one was likely ever to learn more abiut 

 them. Thus Eocidaris was, one hoped, quietly laid on the 

 shelf. 



It now seems advisable to defend in greater detail the 

 conclusions set forth in my memoir with a brevity that might 

 have been praiseworthy had everyone been prepared to 

 accept them. 



Desor (1856, ' Synopsis,' p. 155) based the genus Eocidaris 

 on interambulacral plates and radioles, " Ces plaques ^tant 

 hexagonales, elles doivent par consequent rentrer dans la 

 tribu des Tesselles. Un gros tubercule par plaque. Cii 

 lubercule est ^ base lisse et perform au sommet, mais il'diff^re 

 de ceux du genre Archaocidaris par I'absence d'un second 

 anneau. Ambulacres inconnus. Radioles gr^les, garnis de 

 petites e|)ines sporadiques." It is clear from this that, not 

 only was Eocidaris delined as one of the Tessellati, but that 

 it belonged to the Family now called Archreocidaridfe or 

 Lepidocidarida\ In short, the generic concept was })recisely 

 that which has subsequently given rise to Cidarotropus (see 

 Bather, Nov. 1907). 



To Eocidaris Desor referred six species, in an order 

 governed by their stratigraphical position, the newest coming 

 first :— 



[C'idaris] kaiserlingii [sic] Geinitz. Lower Zechstein. 



Palcechinus lerneidllanus King. Permian. 



C'idaris rossica Biich. Carboniferous. 



Echinocrinnx munsterianus Koninck, M'Coy. Carboniferoua. 



C'idaris lavisjmia Sandberger. Devonian. 



Ciduris scrobicnlata Sandberger. Devonian. 



Of these species C. rossica was included with doubt, 

 since Desor was not certain that the plate was hexagonal. 

 E. munsterianus was placed here only on the doubtful evidence 

 of a radiole. It therefore follows that the genotype, when- 

 ever selected, must be one of the other four species. 



We have now to see what action has been taken by subse- 

 quent authors. 



H. B. Geinitz (1861, p. 108) accepted Desor's reference 

 of Cidaris heyserlingi to Eocidaris, and said that the inter- 

 ambulacrals were " sehr deutlich sechsseitig," but his figures 

 (Taf. XX. figs. 7, 8, 9) show plates tiiat are obviously five- 

 sided. The same author (1866, p. 61), describing a new 

 species, Eocidaris hallianus, did not discuss the genus in any 

 way. 



J. Hall (1867-70, p. 341) referred Echinus drydenensis 



