292 



PALEONTOLOGY OF ILLINOIS. 



29 - This species seems to be related to P. 



pyramidalis, of Lyon and Casseday (Am. 

 Jour. Scl, 2d ser , vol. 29,^. G9), but dif- 

 fers in the proportions of the calyx below 

 the arms, its height and breadth being as 

 84 to 33, -while in P. 2W am ^ a ^ s ) the 

 same measurements are given as 80 to 18. 

 Its first radial plates are also proportion- 

 ally much higher, and less concave above, 

 judging from Messrs. Lyon and Casseday's 



Pterotoerinus crassus. — (Nat. size.) descrintion 



This diagram shows the arrangement of the 

 basal, radial and anal pieces; and in two of the r 7 . , . , __ 



rays, the secondary radials, brachial pieces LiOcallty and position : Hardin county, 



Illinois, Chester group; Subcarboniferous. 



and commencement of the arms. 



Pterotocrinus chesterensis, M. and W. 



PL 23, fig. la, lb, Ic. 



Dichocrinus [Pterotocrinus) chesterensis, Meek and Worthed, Sept., I860. 

 Acad. Nat. Sci., Philad., p. 383. 



Proceed. 



Body below the arms rather small, basin-shaped, or more 

 than twice as wide as high, widening rapidly upwards from 

 the base, the sides being slightly concave in outline; composed 

 of moderately thick, apparently smooth plates, which are con- 

 nected by linear sutures. Base more than one-third as broad 

 as the body, about three times as wide as high, truncated and 

 concave below; the concavity being margined by an angular 

 rim; columnar facet small, or less than one-third as wide as 

 the truncated under side of the base. First radial plates about 

 the size of the basal pieces, though proportionally higher, twice 

 as wide as long, and widening rather rapidly from below; four 

 of them quadrangular and one on the anterior side pentagonal; 

 all distinctly concave on the upper side (which is longer than 

 either of the others), and having their salient upper lateral 

 angles slightly truncated for the reception of small interradial 

 pieces. Second radial pieces minute or merely rudimentary, 

 triangular, and each partly supporting on its sloping upper 



