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



Unio Jialeiamis Lea. Trans. Am. Philos. Soc, Vol. 

 VIII, p. 247, PL XXVII, Fig. 63, 1842. Also a form 

 said to be this is figured by Reeve, Unio Plate XXIV, 

 Fig. 116, 1865, in Conchologia Iconica. There is no 

 resemblance to Lea's form. 



Unio approximusljQ^. Trans. Am. Philos. Soc., Vol. 

 X, PI. V, Fig. 13, p. 74. Described in 1845 from the 

 Red river, Louisiana; published as above in 1848. 



Unio distans Anthony. Am. Jour, of Conchology, 

 Vol. I, p. 156, 1865. 



Unio affinis Lea. Trans. Am. Philos. Soc, Vol. X, 

 p. 271, PI. XIX, Fig. 26; Reeve, Conchologia Iconica, 

 Vol. XVI, Unio Plate LXI, Fig. 307, 1868. Described 

 from Alexandria, Louisiana. 

 Obtained by us in the St. Francis river, at Wittsburg ; and 

 in the Saline river, at Benton. The Benton form is Unio 

 hydianus Lea and is a very abundant one in the Saline. 

 The original description of Lamarck was as follows: — 

 *' U testa ohlongo-ovata, tenui subpellucida, luteo-virente, 

 radiata; latere antico majore^ latiore, rotundato, 



** Habite la riviere Susquehana et celle Mohancks, dans les 

 Stats Unis. * * * La ligament passe entre le crochet et 

 la charniere. Largeur 69 millimetres.''' 



This short and imperfect description was not known to the 

 earlier students of American mollusca,and there is little wonder 

 that considerable synonymy has been established on this &hell. 

 It has a very wide range, extending from Winnipeg and Slave 

 Lakes and the Saskatchewan river, British America, to central 

 New York, south to Georgia, Alabama, Texas ; west to Kansas, 

 Montana and Dakota. In all this range it is abundant in fav- 

 orable localities and often attains a great size. Lamarck's 

 original specimens did not approach the maximum dimensions 

 which this shell sometimes reaches. 



A very beautiful and somewhat depauperate form occurs in 

 the lakes of northern Indiana. It was a specimen of this sort 

 that constituted the basis of Anthony's description of Unio 

 distans. Though sometimes confounded with Unio ligamen- 

 tinus Lamarck there is really no excuse for the confusion of 

 the two forms, since they are more dissimilar than alike. The 



