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



a transverse row of smaller pits or crenulations diminishing 

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

 described and the name P. nJiumanlanus 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 

 80 much doubt as to be considerably perplexed respecting the 

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

 Shumardianus, of Winchell, agrees so nearly with Avicula 

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

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

 Aviculopecien limaformis, that we strongly suspect all belong 

 to the one species Oooperenns.^^ 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 Meekt 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 EntoUum 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 seeinor 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 belong to one 

 species, also including our shell. * * * Again it certainly 

 bears very close relations to Avicida Gooperensis Shumard, 



* Geol. Surv. 111. 3 : 453. 



t Bep. Geol. Surv. Ohio 2' : 292. pi. XV. f. 4a-b. 



