SHELLS OF LAKES AND STREAMS 



303 



a good deal. Hence it has been described on this 

 Coast and Europe under over a hundred names. 

 The American varieties are discussed bv the writer 

 elsewhere and the three best marked retained; these 

 are the typical form, A. c. ber'mcihina^ Midd., and 

 A, c. impura^ Say. 



The typical shell is buff or green-brown, inflated, 

 sub-elliptical, with low umbos, and a straight, nar- 

 row, toothless hinge-line. Within it is iridescent 

 blue or pearly-white. This form is the common one 

 in Eurasia and the Columbia and Klamath Systems. 

 It is found occasionally farther south. 



The common southern form, Anodonta cygnea 

 impura^ Say {A. wahlamatensis^ A. nuttalliana^ A. 

 calif orniensis)^ the Winged Naiad, Figure 288, is 



Fig. 288 



