668 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



PLANUS GROUP. 



Calyx elongate ; the plates thin and without ornamentation ; upper faces 

 of the radials straight, or very little sloping toward the angles. 



Platycrinus planus 0. and Sh. 

 Plate LXIX. Figs. 2a, b, c, d. 



1830. Owen and Shumaud ; Journ. Acad. Nat. Sci. Pliila. (qbw series), Vol. II., Parts I. and II., p. 57 ; 



also U. S. Geol. Surv. Minn., Iowa, and Wise., p, 587, Plate iA, Kg. ia (not ib = P. 



Tfutteni). 

 18S1. W. and Sp. ; Revision, Part II., p. 74 (Proceed. Acad. Nat. Sci. Phila., p. 248). (not P. planus 



Hall, Geol. Rep. Iowa, Vol. I., Part II., Plate 8, Pigs. 6a, h^P. Halli ; nor P. planus, Meek 



and "WojiTnE,\', Geol. Rep. Illinois, Vol. III., Plate 16, Fig. 6 = P. Pratteni). 

 Syn. Plali/eriims hloomfieldensls S. A. Miller, 1879; Journ. Cinciu. Soc. Nat, Hist., Vol. II., Plate 



15, Pig. 4. 



A moderately large species. Calyx elongate. Dorsal cup goblet-shaped, 

 higher than wide in large specimens, height and width about equal in 

 smaller ones ; basal cup deep, obconical, slightly truncate at the bottom ; 

 radials a very little spreading to the facets, the latter projecting so as to 

 give to the cup, as seen from above, a slightly pentagonal outline. Plates 

 thin and perfectly smooth ; the suture lines rather indistinct. 



Basal cup large, obconical, its height eqiial to two fifths the height of the 

 dorsal cup ; the lower face slightly truncated but not excavated, obscurely 

 elliptic, and covered completely by the column. Eadials longer than wide, 

 the sides almost parallel ; the limbs somewhat inflected and knife-like at 

 their superior edges, where they form almost a straight line with those of 

 adjoining plates ; the median portions of the plates slightly thickened, thin- 

 ning out gradually towai'd the sutures. Width of the facets one third the 

 diaiueter of the plates; horse-shoe-shaped, deeply excavated, and fiicing up- 

 wards. Costals short, trigonal, occupying the whole width of the facets, 

 their sloping upper faces concave. Distichals twice as wide as long, and 

 as long as the costals ; the lower ones of the same ray in sutural contact. 

 Palmars and post-palmars three fom-ths as long as wide, their lower j^lates 

 connected by suture. Arms four to each subdivision ; or eight to the raj' ; 

 very long, rounded on the back, and but very slightly decreasing in width. 

 The arm joints moderately short, the intervening suture lines distinctly 

 waving. Pinnules long and in close contact laterally. The ventral disk, 

 so far as observed from the fragments preserved, extends up almost vertically 



