342 REPORT ON THE STATE CABINET. 



areas, each consisting of two continuous ranges of medium-sized 

 pentagonal plates bordering the ambulacra, and two or more ranges 

 of hexagonal plates ; some of the latter ranges becoming obsolete 

 before reaching the extremities of the areas. Plates of the inter- 

 ambulacral areas, with their centres occupied by a single rounded 

 tubercle for the attachment of a spine. No elevated ring surrounding 

 the tubercle has been observed. Spines of medium length, slender, 

 muricated. Ovai-ian apertures dorsal. Oral aperture ventral, cen- 

 trally situated. 



This genus is intermediate in characters between Palechinus, Scouler, 

 as given by M'Coy (^Synopsis of Carboniferous Fossils of Ireland, p. 171), 

 and Arch^ocidaris, M'Cot = Echinocrinus, Agassiz, = Pal^ocidaris, 

 .Desor [Idem, p. 173]. From the former it differs in having a central 

 tubercle and only one spine on each plate, features which are made 

 prominent among the generic characters. From the latter genus it differs 

 in having the interambulacral areas composed of a larger number of 

 smaller plates, with the central ranges becoming obsolete before reaching 

 the extremities of the areas ; while those of Arch^ocidaris gradually 

 decrease in size, but reach to the top and bottom of the interambulacral 

 fields. 



The following is Mr. Desor's description of the Genus Eocidaris : 



"EociDAEis, nov. geu. Like the Genus Ajjchjlocidaeis, this geuus is yet 

 known only by some plates and some spines. These plates being hexagonal, 

 they should consequently be placed in the tribe of the Tesselates. One large 

 tubercle on each plate. This tubercle is smooth at the base, and perforated at 

 the summit; but it differs from those of the Genus Arch^ocidaeis in the 

 absence of a second ring. Ambulacra unknown. Spines slender, ornamented 

 with small sporadic spines. 



"Found in Devonian, Carboniferous and Permian strata." 



It is probable that some of our American species, heretofore referred to 

 the Genus ARCHiEOCiDARis, will prove to belong to this genus ; and since 

 they can be determined by the character of the separated plates and 

 spines, there will be little difficulty in the identification. 



