THE FAMILY NAIADES. 41 



Being unacquainted with the following species, I have 

 deemed it best simply to insert a list of them, with the hope 

 of their being determined at a future period : — 



Unio rubens, Menke. 



Unio rugatus. Menke. 



Unio Grccnlandicus.* Schru. Fer. 



Unio orientalis. Fer. 



Unio nitidens. Fer. 



Unio obtusus. Fer. 



Unio preciosus. Fer. 



Unio pulchellus. Fer. 



Unio purpuriatus. Say. 



Unio musivus.* Speng. 



Unio gibbus,* Spe7ig. 



Unio truncatus.* Speng. 



Unio oviformis. Con. 



Unio furvus. Con. 



The following species are supposed to exist in a fossil state. 

 As the casts only are usually observed, it must be a matter of 

 great doubt as to the propriety of making species where that 

 is the case : — 



Unio crassiusculus. Sow. Flem. 



Unio concinnus. Soiv. Flem. 



Unio uniformis. Sow. Flem. 



Unio acutus. Sow. Flem. 



Unio Listeri. Sow. Flein. 



» On the authority of Ferussac. 



