26 Trans, Acad. Sci. of St. Louis. 



a transverse row of smaller pits or crenulations diminishing 

 outwards. At the same time the new species P. limatus was 

 described and the name P. shumardayius given to the Avicula 

 circulus of Hall, it being pointed out that Hall's shell was not 

 identical with Shumard's species. The characteristic car- 

 tilage pits of the genus were observed only in the type species, 

 the other two species being placed in the genus because of 

 their strong outward resemblance to the type. 



In 1868 Meek and Worthen* identified with a query, a 

 shell from the oolitic bed of the Kinderhook Group at Bur- 

 lington Iowa, with Pernopecten shumardanus. They say: 

 ** In regard to the true relations of this shell to forms that 

 have been described under several other names, we are left in 

 so much doubt as to be considerably perplexed respecting the 

 proper disposition to make of it. * * * , the species 

 ShumardianuSy of Winchell, agrees so nearly with Avicula 

 CooperensiSf of Shumard, which we believe to be the same since 

 described by Dr. White and Mr. Whitfield, under the name 

 Aviculopeclen limaformis, that we strongly suspect all belong 

 to the one species Cooper ensis.^^ The crenulated hinge-line of 

 Pernopecten was not observed by Meek and Worthen in any 

 of their specimens, the generic reference being made wholly 

 upon outward resemblance. 



In 1876 Meekf identified a shell from the Waverly Group 

 at Richmond and Lodi, Ohio, with Winchell' s P. shumar- 

 danus. It was identified with a query, however, and was 

 referred to the genus Entolium instead of Pernopecten, 

 because of the supposed absence of the crenulated hinge-line. 

 Prof. Meek expresses doubt as to the true specific relations of 

 the shell, saying, ** It perhaps agrees most nearly with Prof. 

 Winchell' s description of his Pernopecten Shumardianus. 

 But after seeing how these shells vary in the slight details of 

 form and their obscure surface markings, it seems to me quite 

 as probable that it may belong to his P. limatus, or rather 

 that the latter and P. shumardianus mav both belone: to one 

 Species, also including our shell. * ♦ * A^ain it certainly 

 bears very close relations to Avicula Cooperensis Shumard, 



♦ Geol. Surv. 111. 3 : 463. 



t Rep. Geol. Surv. Ohio 2» : 292. pi. XV. f. 4a-b. 



