Notes on Species of Corbiculadm. 



63 



a violet under surface. The valves are moderately solid, they 

 are curved in the centre but very much flattened on the inferior 



Fiu. 7. 



Fto. a 



i _ ~JW— ^ 



Corbicula difficilis. 



Oorbicula cor. 



margin and its immediate vicinity. The interior is violet. 

 The lunge is moderately broad and strong, and is curved. The 

 strise are more or less regular, they are not much raised. The 

 epidermis is somewhat polished and is of a dusky greenish color. 

 A peculiarity of this species is the remarkable appearance 

 presented by the inferior portion of the valves, the lower margin 

 of the shell, starting from the inferior extremities of the lateral 

 teeth, is so much flattened as to induce one to suppose that the 

 compression was due to artificial means ; this can, however, 

 hardly be the case, as a number of specimens which I have had 

 under examination showed exactly the same characters. The 

 Corbicula difficilis has probably been confounded with Corbi- 

 cula cor, and looked upon as an abnormal variety of that spe- 

 cies. On comparison, however, we find that the species differ 



