456 PALEONTOLOGY OF ILLINOIS. 



side a A r ery small pinched projection on each arm piece ; the longer 

 diameter of these little projections being ranged transversely outward 

 and inward. 



This form has sometimes been confounded with P. planus, of Owen 

 and Shumard, but it differs in having much thicker body plates, those 

 of that species being very thin and fragile. The sinuses in its first ra- 

 dial pieces for the reception of the second are also deeper in this than 

 in P. planus, while the first radials of that species have their upper 

 lateral margins straight out to the suture, and not truncated as in this, 

 to form a notch for the reception of the subradial and anal pieces. So 

 far as we have been able to ascertain P. planus seems also to differ in 

 having the opening of its vault in a much more prominent, if not pro- 

 boscidiforrn projection. Its second radial pieces and the others between 

 these and the bifurcations of the rays also differ from those of the form 

 under consideration in not being directed out horizontally. 



From P. cequalis, Hall, this species differs in having a regularly 

 rounded, or subhemispherical base, and less convex first radial pieces; 

 while its arms, as indicated by specimens apparently belonging to the 

 same species as the figured specimen, are entirely different from those 

 of P. cequalis. 



The specimen figured by Prof. HALL, on plate 8, of his Iowa Eeport, 

 under the name P. planus ? , is certainly not that species, but has the 

 thick plates, and other characters of the form under consideration, ex- 

 cepting that it has obscure undulations on its basal and first radial 

 pieces, not seen on P. Halli, and hence may be new. 



Locality and position Upper part of the Burlington division of the 

 Lower Carboniferous series, at Burlington, Iowa. The specimen figured 

 belongs to Mr. WACHSMTTTH'S collection. 



PLATYCEIKITES ^EQTJALIS, Hall. 



PI. 3, Fig. 8. 

 Platycrinus cequalis, HALL, 1861. Desc. !N"ew sp. Crin., Prelim. Note, p. 17 



BODY rather deeply cup-shaped, rounding below to near 

 the facet for the attachment of the column, which is elliptic 

 and somewhat protuberant, so as to give the sides of the 

 base just above, a slight concavity of outline. Base some- 

 what basin-shaped, rather more than twice as high as wide, 

 and forming more than one-third of the hight of the body 

 to the top of the first radial pieces; sutures anchylosed, 



