FRESHWATER AND LAND SHELLS. 81 



Hab. Wahlamat, near its junction with the Columbia River. Pro- 

 fessor Nuttall, 



My Cabinet. 



Cabinet of Professor Nuttall. 



Diain. 1, Length 1*8, Breadth 3'2 inches. 



Shell somewhat winged, elliptical, rather inflated, inequilateral ; sub- 

 stance of the shell thin ; beaks scarcely prominent and undulate at tip ; 

 epidermis somewhat shining and striate ; posterior and anterior cica- 

 trices both confluent ; dorsal cicatrices placed in the centre of the ca- 

 vity of the beaks ; cavity of the shell rather deep ; cavity of the beak 

 very small ; nacre white. 



. Remarks. — Another species for which I am indebted to Professor 

 Nuttall, procured in his late journey. It has some resemblance to Jin. 

 cygnea, but is still more closely allied to An. Benedicfensis (nobis). 



Angdonta exilis. Plate XXII. fig. 68. 



Testa latct, valdh compressd, incequilaterali ; valvulis tenuibus ; natibus vix prominulis ; 

 epidermide glabra ; margarUd ceruled et iridescente. 



Shell wide, very much compressed, inequilateral ; valves very thin ; beaks scarcely 

 prominent ; epidermis smooth ; nacre bluish and iridescent. 



Hab 



My Cabinet. 

 Diam. -8, Length 1-6, Breadth 3*4 inches. 



Shell wide, very much compressed, slender, rounded before and an- 

 gular behind, inequilateral ; dorsal and basal margin nearly parallel ; 

 substance of the shell very thin ; beaks scarcely prominent ; ligament 

 long and thin ; epidermis smooth, brown, apparently without rays ; an- 

 terior cicatrices distinct; posterior cicatrices confluent ; dorsal cicatrices 

 posterior to and below the cavity of the beaks; cavity of the shell wide 



YI. — V 



