294 PALEONTOLOGY OF OHIO. 



radiating costae seen on Shumard's figure, as I have elsewhere explained, 

 are also made much too strong by the engraver, even for the individual 

 specimen there represented, while in a great majority of specimens no 

 traces of them whatever are to he seen. In looking over a large collection of 

 specimens of P. Cooperensis, sent by Dr. Williams, of Booneville, Mis- 

 souri, to the Smithsonian Institution, from the same locality and bed 

 from which Dr. Shumard's original typical specimens were obtained, I 

 could only discover faint traces of radiating costse on two or three of 

 them, while all of the others were as completely destitute of any such 

 costse as the specimen from which our figure 4a was drawn. 



At one time I strongly suspected that Aviculopeden limiformis of White 

 and Whitfield, the type of Pernopecten, Winchell, might also be the same 

 species as Avicula Cooperensis, Shumard; but on examining the speci- 

 mens of the latter mentioned above, I was unable to discover any traces 

 whatever, in any of them, of the crenate character of the hinge seen in 

 the type of Pernopecten. 



Some years back. Prof. Winchell did me the favor to loan me the type 

 specimens of his genus Pernopecten, and I made careful drawings of two 

 of them, one of which shows the crenate character of its binge very clearly, 

 while the other gives as satisfactory a view of the exterior. They are both, 

 I think, right valves, and the one showing the hinge agrees almost exactly, 

 in all specific characters, with the form represented by our figure 46, 

 though it is proportionally not quite so broad, and has slightly more ob- 

 tuse ears, while the other agrees even more closely in form with our fig- 

 ure 4a, excepting in having its hinge straight, which, I think, is due to 

 the fact of it being a right valve. Again, Prof. Winchell's type actually 

 seems to agree exactly, in all constant specific characters, with Entolium 

 aviculatuv^ (==Pecten aviculatus, Swallow), already mentioned, from the 

 Coal Measures. So we have here a remarkable case of shells presenting 

 extremely little or no constant specific difference, and yet differing in a 

 character of the hinge that seems to be of generic importance- 



Locality and poniion : The specimen from which our figure 4a was drawn came from 

 the Cuyahoga shale of the Waverly group at Richmond, Ohio, and that represented 

 by figure 46 came from the Waverly group at Lodi, Ohio. Prof. "\Mncheirs type 

 specimens of E. Shumardianus and E. limatus came from the yellow arenaceous beds at 

 Burlington, Iowa, and I believe he has identified the same forms at this horizon in 

 Michigan. 



