have not seen the animal, but the shell I have, in 

 the cabinet of the Academy. 



SPECIES LXI. Alasmidonta costata. 



Shell thin, elliptical, slightly ventricose ; some- 

 what sinuous anteriorly ; undulated with broad 

 curved ribs posteriorly ; epidermis almost smooth, 

 olive coloured anteriorly, blackish posteriorly ; 

 nacre white, tinged with flesh colour ; tooth bi- 

 lobed, compressed, oblique, crenulated. Length 

 i diam. axis f of the breadth. 



I observed this fine shell in the museum of 

 Mr. Clifford of Lexington, Ky. from the Ken- 

 tucky river, where it appears to be rare ; breadth 

 nearly five inches ; decorticated anteriorly and su- 

 periorly, but very entire posteriorly ; ribs very 

 large inferiorly ; ligament horny and shelly, im- 

 bricated ; tooth decurrent ; in the place of the la- 

 mellar tooth a small, short, oblique angle ; small 

 tubercles in the interior. 



FIFTH SUB-FAMILY Cycladia. 



Shell almost equilateral, two lamellar teeth ; 

 one anterior, the other posterior ; often one or 

 more cardinal teeth intermediary, under the 

 apex. 



