THE FAMILY NAIADES. 



21 



TRIANGULAR. 



pyramidatus. Lea. 

 Unio rubra? -S«/! 

 Unio mytiloides. Con. 



mytiloides.* Raf. 

 Mya obliqua. Wood. 



OBLIQUE. 



Troostensis. Lea. 

 Unio trabalis. Con. 



Tigris. Fer. 



Taitianus. Lea. 



cor. Con. 



truncatus. Swain. 



decisus. Lea. Con. 



* The difficulty of recognising Mr. Rafinesque's species is well illustrated 

 in this one. Mr. Conrad considers triangularis, Raf., as the type, and gives 

 the following names of the same author as synonyms, viz. : lateralis, iin- 

 toxia, pachostea, mytiloides, and rubra; thus charging him with making 

 six species of one. But what is still more extraordinary, this single species, 

 (agreeably to Mr. Conrad's synonyms,) is not only divided by Mr. R. into 

 different subgenera, but into different genera, and even into two different 

 SUBFAMILIES ! ! See New Fresh Water Shells of the United States, p. 72. and 

 Mr. Rafinesque's " Monographie." In Mr. Say's " Synonymy," triangularis, 

 Raf., is considered to be the same as ellipsis ! (nobis.) 



