114 THE NAUTILUS. 



PLEUROSEMA LEWISII (LEA). 



BY BRYANT WALKER. 



As the result of some recent correspondence between Mr. L. 

 S. Frierson and the writer, it has become evident that the 

 synonymy, in which this species was included by Simpson in 

 his Synopsis and Descriptive Catalogue, will have to be revised. 

 We are both of the opinion that this species is entitled to specific 

 recognition for the following reasons. 



The synonymy given by Simpson is briefly this : 



1834. Unio mytilloides var. Conrad. Type locality, Alabama 

 River. 



1834. Unio cor Conrad. From the Elk and Flint rivers, Ala. 



1861. Unio crapulus Lea. Type locality, Etowah River, Ga. 



1861. Unio lewisii Lea. Type locality, Coosa River, Ala. 



Just what Conrad's mytilloides var. was, is not certain. If it 

 was not a Pleurobema, it is entirely immaterial what it was so 

 far as the species under consideration is concerned. But it was 

 apparently a Pleurobema from the Alabama River. If so, it is 

 equally immaterial what it was, so far as nomenclatorial pur- 

 poses are concerned. In 1820 Rafinesque described a species 

 from the Wabash as Pleurobema mytilloides. As in the case of 

 so many of the species described by this author, there has al- 

 ways been an element of uncertainty as to what his species really 

 was. By a general concensus of opinion among the earlier stu- 

 dents of American Unionidas, it was considered to be the same 

 as the species subsequently described by Lea as Unio pyramida- 

 tus. Dr. Lea, himself, gave it doubtful recognition as a valid 

 species and placed it near pyramidatus in his Synopsis. Simp- 

 son states that, in his opinion, the shells under this name in the 

 Lea collection are an elongated form of pyramidatus. Conrad 

 in his Synopsis of 1853 considered it a synonym of Lamarck's 

 clava. It is quite probable that he was entirely correct in this 

 disposition of this species, which would be a very satisfactory 

 solution of the problem. It seems to be reasonably certain, 

 however, that it was either clava Lam. or pyramidatus Lea. Ac- 

 cording to Dr. Ortmann, pyramidatus Lea is a Pleurobema and 



