Call — The Unionidon of Arkansas. 9 



Little Red river, in Van Buren county, one fine example of 

 which we have seen, together with a poorer one. It came to us 

 under the name of Unio arkansasensis Lea. From Claiborne 

 Parish, Louisiana, we have seen about fifty »ood examples. 

 The large and old shells resemble much some forms of Unio 

 ellipsis Lea. 



Unio cerinus Conrad. 



Monograph of Unio, p. 95, Plate LII, 1838. Reeve, 



Conchologia Iconica, Vol. XVI, Unio^ Plate LXXXVII, 



Fig. 468. 

 The only Arkansas example which we have seen was taken 

 in the Little Red river, and was loaned to us for examination 

 by Mr. W. A. Marsh. It is a fine female and a very charac- 

 teristic form. Mr. Lea makes this shell a synonym of his Unio 

 rubiginosus, but does so wrongly. Before us are forty or more 

 specimens from Louisiana, the original home of the species, 

 some of which are sufficiently perfect to disclose undulations on 

 the beaks such as no rubiginosus ever possessed. They rather 

 ally Conrad's shell to those peculiarly marked Mexican and 

 Central American forms that have similar beaks. No shell 

 with which I am acquainted so well presents similar characters 

 as the common Texan form to which Gould gave the name of 

 Umo petrinus, the original examples of which came from 

 Mexico. This species will certainly not fall under rubiginosus 

 whatever else may become of it. 



Unio clavus Lamarck. 



Plate I. 



This shell is one of those prolific sources of synonymy with 

 which the descriptive matter of American fresh-water couchol- 

 ogy has become so burdened. In the hope that it will subserve 

 a useful purpose the original description of Lamarck follows, 

 and the synonymy as now understood, excepting only those 

 names which have not been accompanied by figures. 



The following description is taken from Volume VI, " His- 

 toric Naturelle des Animaux sans Vertebres," page 537, 1838. 



" U. testa sublongiiudinalii oviformi, inferne fumida, 

 obtusa; postico latere brevissimo; dente laterali prcelongo. 



