82 rafinesque's 



Var, 1. Viridis. Green outside. 



Var. 2. Fuscata. Brown outside. 



Var. 3. Zonalis. Witli green and brown zones. 



River Kentucky and Green, the largest and finest sp. of the 

 West, reaching 5 and 6 inches, hinge almost without any visible 

 fold. 



113 Sp. Anodonta digonota. (Lastena digonoia, 1826.) Shell 

 thin, oval swelled, back straight, obliqual, with two angles, one 

 before and one behind, similar to small wings, sloping behind, with 

 a flexuose edge ; outside laminated, pale, olivaceous, inside bluish 

 white, iridescent. Length 5-8, diameter 3-8, axis 1-4 of the 

 breadth. 



From Lake Erie, two inches, hinge inside, with a flexuose fold, 

 separated from the straight back. Perhaps a peculiar S. G. 

 FlexipUs. 



I have besides, another doubtful Anodonta ; A. riifa, probably a 

 var. of ^, ohiensis, sp. 58. 



V. Genus or tribe, CYCLAS. 



I have no new sp. of Cyclas ; but I am enabled to present a beau- 

 tiful new genus of this tribe, which forms the passage between Unto 

 and Cyclas. ' I call it Dvplasma, meaning double lamellar teeth. 

 The specimen before me, was not collected by myself; it belongs to 

 the cabinet of shells of Mr. Hembel, of this city, who has had the 

 goodness to lend it to me. It is labelled Unio, and is supposed to 

 come from the river Tennessee, which I am inclined to doubt, because 

 I have in my cabinet, a specimen nearly alike, from the river Ganges, 

 collected by Dr. Burroughs, and because the G. Diplasma appears 

 to be Asiatic. I therefore suspect that this species of Mr. Hembel, 

 is also from Hindostan, and shall therefore include it in the 

 following 



APPENDIX. 



On eight Asiatic bivalve fluviatile shells. 

 These shells were all collected in the rivers of Hindostan, by Dr. 

 Burroughs of this city. They appear very different from our North 

 American shells, forming even often peculiar genera. They are 3 

 sp. of Diplasma, 1 sp. Loncosilla, 2 sp. Lampsilis, and 1 

 Ohliquaria. 



