124 PALEONTOLOGY OF OHIO. 



ECHINODERMATA. 



CBINOIBEA. 

 Genus PLATYCRINCJS, Muller. 



Platycrinus peematcirus (n. sp.). 



Plate 6, fig. 3-6. 



Body of medium size, depressed oblate, and in a basal view strongly 

 pentalobate, from the thickened tumid character of the first radial plates, 

 which form the largest or widest part of the body^ and above the middle 

 of which the cup is strongly and rapidly contracted to the arm bases. 

 Basal plates large, but forming only a small proportion of the height of 

 the cup, their centers tumid, and projecting below the top of the column 

 in the form of three strong, rounded nodes, the sutures between being 

 strongly marked, but not abrupt. First radial plates large, much wider 

 than long, and equal in height to about one-half of that of the cup ; 

 their upper lateral angles truncated by the interradial plates, and the 

 centers excavated for the reception of the second radials, between which 

 and the interradial plate the lower end of the supraradial plate on each 

 side reaches to and rests upon the first radial. Second radial very small, 

 rounded, triangular, pointed above, and higher than wide; occupying 

 the center of the upper margin of the first radials, and not more than 

 one-quarter of the width ; supporting on each of the two upper sloping 

 faces one side of the first supraradials, which meet above the point, the 

 lov/er end resting on the first radial, and the outer side against or on the 

 interradial plate. On the upper faces of the first supraradials rests a 

 second pair, which are excavated on their upper sides for the plates of 

 the arms. Interradial plates proportionally large, the general appear- 

 ance being that of a triangle, higher than wide, but in reality they are 

 hexagonal, resting on the two adjacent first radials and between the first 

 supraradials of the adjoining rays, and supporting two smaller plates on 

 the upper faces and between the second supraradials of the two adjacent 

 rays. 



Surface of the basal plates tuberculose ; the tubercles having their 

 longest diameter in the direction of the greatest length of the plate. 

 Surface of the first radials much thickened and tumid, the tumidity ex- 

 tending to the margins of the plates and occupying the entire surface. 

 x\bove the first radia^ls the plates are strongly convex, but do not ap- 



