THE NAUTILUS. 115 



Dot a Quadrida. But even this is immaterial, if Rafinesque's 

 species can be satisfactorily identified as either of those species. 

 If mytilloides Raf. is the same as clava Lam., it disappears in the 

 synonymy. If it is the pyramidatv.s Lea, it would take prece- 

 dence of that species. But in either event, and that is the im- 

 portant point here, the specific name mytilloides can not be used 

 again for a different species of Pleuroheina. So that, although 

 Conrad's mytilloides was described as an Unio, his name, even if 

 the species is clearly identified, can not be used if his type was 

 a Pleurobema. 



The shells, on which Conrad based his Unio cor, came from 

 the Elk and Flint rivers, Ala. Both of these streams are tribu- 

 taries of the Tennessee River. It is probable that the form 

 described by Conrad as cor represents some species also described 

 by Lea. Mr. Frierson has investigated that question (Nautilus, 

 Jan., 1916, p. 102). But whatever U. cor is, it is quite clear 

 that it is not the same as either of Lea's species, crapidus or 

 lewisii. With the great increase in recent years of our knowl- 

 edge of the faunas of the Alabama and Tennessee drainage 

 systems, it has become more and more evident that there are 

 ver}^ few species of Pleurobema that are common to both systems. 

 The fauna of the Tennessee has been very thoroughly worked 

 over and there can be no doubt that there is no species in that 

 fauna that can by any approximation be referred to either of 

 Lea's species. 



The elimination of cor from further consideration leaves the 

 two species from the Alabama system to be dealt with. As- 

 suming, for the purposes of the argument, that they are synon- 

 ymous, what name shall be used ? Both were described in the 

 same paper, but aripidvs has page precedence. This, however, 

 under the Code (see Naut. xxviii, p. 125), is immaterial. I am 

 of the opinion that precedence should be given to the name of 

 leioisii for the following reasons: 



1. The lexcisii Lea is a well-defined and well-known species of 

 the Coosa, and there can be no doubt as to what it is. 



2. Lea's a-apidus came from the Etowah River, Ga., and was 

 described from a single specimen. It does not seem to have 

 been found by any of the recent collectors. While it may be 



