GENEEA AND aEOTTPS OF THE ECHIlSrOIDEA. 139 



du Dept. de la SartJie, Suppl. p. 412. Cotteaio, Peron et 



Gauthier, 1879, Ecli. foss. de V Alger, fasc. 8, pi. xii. fig. 2. 



Duncan Sj- Sladen, 1886, Jburn. Linn. Soc. vol. xx. p. 48. 



Loven, 1874, Etudes, pi. xiv. fig. 125 ; 1888, Bihang till K. 



Sv. Vet.-AJmd. Kandl. Bd. 13, Afd. iv. no. 10, p. 9. 



Test moderate and large, circular or subpentagonal in marginal 



outline, fiat actinally, hemispherical or couico-liemispherical above 



the margin. 



Apical system small, subpentagonal, the five basal plates united ; 

 the madreporite perforating some or all, genital ducts \\\ all 

 except the posterior ; radial plates small. 



Ambulacra narrow, flush, except actinally, where they are 

 slightly raised, apetalous, consisting of low primaries near the 

 apex, with rare demi-plates: near the ambitus and actinally there 

 are compound plates, made up of a large middle primary, carrying 

 a tubercle, and an adoral and aboral demi-plate, their sutures 

 convex towards the large primary plate ; or a large primary plate 

 is associated with a small adoral demi-plate, the suture being 

 convex abactinally. Pairs of pores very numerous, small, in 

 simple series abactinally, becoming slightly biserial and crowded 

 actinally. Primary tubercles small, crenulated and perforated. 



Interradia with distinct median siitures ; tubercles small, per- 

 forate and crenulate, the vertical rows have larger tubercles near 

 the median line than elsewhere. 



Peristome small, funnel-shaped, its margin high up and formed 

 by ambulacral plates and also by a single plate in three interradia, 

 and by a double plate in two interradia. Perignathic girdle a 

 raised oblique discontinuous ring, composed of interradial plates 

 (a ridge), the upper surface flat or shelving. 



Interradial plates within the actinal surface with radiating ribs. 

 Periproct small, actinal, between the posterior margin and the 

 peristome, its plates large posteriorly and reaching close to the 

 anal opening. Branchial incisions indistinct. 

 Fossil. Cretaceous : England, Europe, N. Africa. 



The morphology of Discoidea subuculus, Klein, necessitates 

 the formation of a subgenus for its reception. 



Subgenus Bchinites (non auctorum). 



Test small, tumid actinally and at the margin, subhemispherical 

 above. 



