22 



University of Michigan 



This identification of the type has no effect if the species 

 has been described satisfactorily in the meantime. Two names 

 of Rafinesque, lateralis and cordatus, should be considered first. 

 The latter has been used for this species by Conrad and an 

 excellent figure been given ; the former has been referred here 

 by Vanatta after examination of the so-called Rafinesque- 

 Poulson "type." 



Conrad's use of cordatus is contradicted again by Vanatta, 

 who says that the supposed type of cordatus is U. pleniis Lea. 

 But this does not agree with the original description and figure, 

 which unmistakably indicate the so-called obliqua Lam. and 

 cordatus of Conrad ('36). It is a triangular, thick, swollen 

 shell, with a sinus on the postero-inferior margin and a depres- 

 sion upon the disk, with brown epidermis and white nacre. 

 The outline of Rafinesque's figure (6) expresses the character 

 of a young "obliqua" very well, and his cordata was a young 

 shell about one inch long. 



"The specimen in the Rafinesque-Poulson collection (No. 

 20221, A. N. S.) is a characteristic Unio obliqua Lam., larger 

 and less rayed than Conrad's (Mon., pi. 25), but agreeing 

 closely with it in form. Mr. Vanatta concurs in this determi- 

 nation. He was formerly misled by some lots of the same 

 form which had been carelessly labelled 'U. plcnus Lea.' " (H. 

 A. P.) 



On the other hand. Obi. lateralis Raf. is also this species. 

 The description indicates a thick, swollen shell of oval, oblique 

 shape, with an oblique, curved depression upon the disk, brown 

 epidermis and white nacre, which is sufficient for its recogni- 

 tion. \''anatta's examination of the so-called Rafinesque-Poul- 

 son "type" has confirmed this. 



Thus, there are two names available for this shell, lateralis 

 and cordata, both recognizable from the original description, 



