656 THE CRINOIDEA CAMEEATA OF NORTH AMERICA. 



the iniddle one of the first row is subtriangular in outline, and as large as 

 four or five of the others together. The middle plate of the anal side is 

 somewhat smaller, and subquadrangular. It is followed by a very large num- 

 ber of minute pieces, which form a circular, well defined, rounded protuber- 

 ance, extending from the orals to the lai'ge quadrangular plate. In young 

 specimens (Plate III, Fig. 16), the orals are as large as in the adult (Plate 

 LXIX., Fig. Ic) ; they are even more regularly arranged, and stand out con- 

 spicuously over the surrounding part of the disk ; the ambulacra are shorter, 

 and the interambulacral spaces consist of only five or six pieces, of which 

 the middle one bears a central node. Column decidedly elliptic, except the 

 proximal joints which are circular, and it has a rapid twist. The length of 

 the stem, as observed in several specimens, does not exceed 15 cm. ; its termi- 

 nal part, after giving off a few short lateral cirri, ends in a sharp jDoint. 



Horizon and LocalUi/. — Kinderhook group ; Le Grand, Marshall Co., Iowa. 



Types in the collection of Wachsmuth and Springer. 



Remarks. — Tliis species differs from P. Agassisi of the same horizon, in 

 the more spreading calj'x, heavier plates, grooved suture lines, and the short 

 and rounded basal cup without projecting rim. 



Platycrinus pileiformis Hall. 

 Plate LXIX. Fig. 6, and Plate LXX. Figs. 13a, h. 



1858. Hall ; Geol. Rep. Iowa, Vol. I., Part II., p. 529, Plate 8, Figs, ia, b, c. 

 1881. W. and Sp. ; Revision, Part II., p. 71 (Proceed. Acad. Nat. Sci. Phila, p. 248). 



Syn. P. carchesium S. A. Millek ; Geol. Surv. of Missouri, Bull. 4, p. 23, Plate 4, Tigs. 6, 7- 



Of medium size. Dorsal cup deep, about as high as wide, somewhat 

 expanding upwards, rounded at the base. Plates rather thin, except the 

 radials below the facets ; surface smooth. 



Basal cup basin-shaped, evenly rounded, its height fully half the length 

 of the radials, the middle portions slightly excavated for the column facet, 

 which is circular ; intei'basal sutures rarely visible. Radials a little longer 

 than wide, the sides almost parallel, the upper faces deeply notched, the 

 notch of the anal side considerably wider and much deeper, giving to the 

 posterior radials an asymmetrical form. Facets semi-circular, less than half 

 the width of the plates, their upper margins but slightly excavated. Costals 

 triangular in outline, generally occupying the full width of the facets, those 

 of the same ray in sutural contact laterally, fully twice as wide as long, and 

 giving off two arms eacli. Arms four to the ray, very heavy, subcylindrical, 



