PALAEOZOIC FOSSILS. 207 



GENUS EOCJDAIMS (Desok). 



Af'JKII a ciircrul jstiidy oi" tJic '^Echinus drydc7iensis^^ of Vanijxkm, it 

 wtiH found to poHHesH certain cliuracterH wliich Hcparatcd it from Aiicilil'io- 

 CIDAKIK, and also from pALKC'lllNdS ; and tlio ^emtric dciscription Ixdovv 

 waH written before 1 liad ob.sisrved itH Kimilarity to tlie (Jenus KuciDAlilK, 

 to wliieh I now propone to refer it. 



Body Hj)lieroidal, eompoHed of five amimlacral and five interam})ulaeral 

 fields. Amhulaera eoiniioscd (jf a double series of plates, each perforated 

 near itH outer extremity hy two Hmall pores. Interambulaeral areas caeh 

 consistin;.^ of two eontiiiuous ranges of medium-sized ])entaf^<»nal plates 

 bordering the ambulaera, and two or more ranges of hexagonal plates; 

 some of the latter ranges becoming obsolete before reaching the; extremi- 

 ties of the areas. Plates of the interambulaeral areas with their centres 

 occupied by a single rounded tu})ercle for tlie atla(;hment of a spine. No 

 elevated ring surrounding the tubercle has been observed. Spines of 

 medium length, slender, muricated. Ovarian apertures dorsal. Oral aper- 

 ture ventral, centrally situated. 



This genus is intermediate in characters between Paleoiiinus ( Scou- 

 LER), as given by M'CoY (Synopsis of Carboniferous Fossils of Ireland, 

 p. 171), and Akcii^ocidarih (M'Coy) z= KonrNOciiiNus (Aqahhiz) 

 = PAliiloociDARiK ( Demor ) [ Idem, p. 1 73 ]. From the former it differs 

 in havirjg a central tubercle and only one spine on each plate, features 

 which are made j)rominent among the generic characters. From the latter 

 genus it diffisrs in having the interambulaeral areas composed of a larcer 

 iiumb(!r of small(;r plates, with tlu; ccintral ranges becoming obsolete bef )re 

 reaching the extremities of the areas; while those of ARCiiiEOOiDARlS 

 gradually decrciase in size, but reach to the top and Ijottom of the interam- 

 bulaeral fields. 



The following is Mr. Dehor'r description of the Oenus Eooidarih : 

 " EoOTDARis, nov. gen. Like tin; (icMius Aroh^eocidaris, this genus 

 ** is yet known only by some plates and some spines. These; plates being 

 ** hexagonal, they should eons(!(jU(!ntly \h\ placed in the; tribe of the Tes- 

 *' RELATE8. One large tubercb; on each jdate. This tubercle is smooth at 

 *' the base, and perforated at the summit; but it differs from those of the 

 *' Genus ARCll.fl?ocn)ARiB in tiie a})sence of a second ring. Ambulacra 

 *' unknown. Spines slender, ornamented with small sporadic spines. 

 " Found in Devonian, Carboniferous and Permian strata." 

 It is pro))a}»l(! tijat some of our American K|)eeies, h(!retofor(! rctferred to 

 the Oenus Arcuteocidarih, will prove to beloiiL' to this genus; and since 

 they can ))e d<;termincd })y the character of the separated plates and spines, 

 there will be liitle difficulty in the identification. 



;{H [ PiibliHhed December I860.] 



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