Weller — KinderhooJc Faunal Studies. 27 



from rocks of the same age in Missouri." As to the relation 

 of the shell to Aviculopecten limaformis W. & W., the type 

 of Pernopecten, Winchell, he says, " At one time I strongly 

 suspected that Aviculopecten limiformis of White and Whit- 

 field, the type of Pernopecten, Winchell, might also be of the 

 same species as Avicula Cooperensis, Shumard ; but on exam- 

 ining the specimens 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 Perno- 

 pecten. * • * So we have here a remarkable case of shells 

 presenting little or 7io constant specific difference, and yet 

 differing in a character of the hinge that seems to be of generic 

 importance." 



In 1884 the type specimen of the genus and species Perno- 

 pecten limaformis, was illustrated by Hall * for the first time. 

 At the same time a specimen from the Waverly Group at 

 Newark, Ohio, called Pernopecten Shumardanus f was illus- 

 trated showing the characteristic crenulated hinge-line of the 

 genus. 



From the above historical sketch it will be seen that confu- 

 sion has always surrounded these species of shells. So acute 

 an observer as Prof. Meek could apparently recognize no con- 

 stant characteristics of the shells from different localities 

 which could be considered as of real specific importance. A 

 few of the shells, however, particularly from the "Yellow 

 Sandstone " at Burlington, Iowa, and a single specimen from 

 Ohio, show a character of the hinge which is apparently of 

 generic importance. Now the question is, did all of these 

 shells possess a crenulated hinge-line when they were living, 

 and is the condition of fossilization such in most cases that it 

 cannot be observed, or do they really belong to two distinct 

 genera, as seems to have been the final conclusion of Prof. 

 Meek? Whatever may be the final decision in the matter, the 

 specific name cooperensis will have to stand either for the 

 whole or only for those without the crenulated hinge-line. 



In none of the Northview specimens have the crenate hinges 

 been observed so that they may be referred safely to the 



• Rep. N. Y. state Geol. 1882. pi. If.l, 2. 

 t Loc. cii.pl. I.f. 3. 



