20 



SYNOPSIS OF 



W 

 o 



H 

 o 



o 

 12; 



w 

 o 



TRIANGULAR. 



gibber. Ze«. 



pumilis. Lea. 



rubiginosus. Lea. 



Barnesianus. Lea. 



pileus. Lea. 



Sowerbianus. Lea. 



solidus. Lea. 



obliqua. Lam. 



Unio undatus. Bar. 



Unio trigonus.* Say and Con.; not oi Lea. 



Unio mytiloides. Eat. 



Unio undulatus. Desk. 



Unio cordatus? i?q/^ 



Unio cordatus. Con. 



* Say and Conrad both give trigonus (nobis) as a synonym to undatus, 

 Barnes. It is difficult for me to understand why they should not at once on 

 comparison be recognised as different species. The trigonus is always more 

 angular on the umbonial slope, and the undulations at the tips of the beaks 

 differ. This may be observed particularly in the young and perfect specimens. 

 If a doubt could be admitted as to the difference of the form of the shell, the 

 colour of the animal in trigonns would at once settle the question. It is 

 peculiar, and differs from all the species I know in being of so deep a colour 

 as to be almost red. 



Some years since, when I described this species, I deposited a specimen in 

 the Academy of Natural Sciences of this city, with its proper name appended. 

 Subsequently, I found the Academy had prefixed the name of undatus, 

 Barnes, to the label, and I presume this error is still continued there. 



