306 ORTMANN— CORRELATION OF SHAPE AND 



Allegheny River. 



Natrona i 52 52 52 lens - 



Godfrey i 51 51 51 lens 



Crooked Creek. 



Rosston 12 59 48 52 lens 



Creekside 5 51 48 50 lens 



The sudden decrease of obesity from the Monongahela to West 

 Fork River is clearly due to the absence of material from a long 

 stretch in the Monongahela. Also in the Allegheny the change is 

 rather abrupt, due to scarcity of material. The gradual transition 

 of the two forms is, however, quite evident in the Beaver-drainage. 



Loc. No. Max. Min. Av. 



Beaver River. 

 Wampum 14 64 49 53 lens (subr.) 



Shenango River. 



Harbor Bridge 3 56 50 53 lens 



Pulaski 2 58 49 53.5 lens 



Clarksville 7 54 48 51 lens 



» 



Also in Elk River in West Virginia this is seen. 



Loc. No. Max. Min. Av. 

 Elk River. 



Shelton i 67 67 67 siihr. 



Clay 2 62 60 61 suhr. 



Gassaway 7 70 56 61 subr. (lens) 



Sutton 9 65 53 58 lens (subr.) 



Some material from the Little Kanazvha also fits into the scheme, 

 but it should be pointed out that the locality on Hughes River, 

 although not quite so far upstream as the others, surely is in the 

 smaller stream. 



Loc. No. Max. Min. Av. 



Little Kanawha River. 



Grantsville 2 68 59 63.5 snbr. (lens) 



Burnsville 5 59 50 53 lens 



North Fork Hughes River. 

 Cornwallis i 50 50 50 lens 



Group of Obovaria subrotunda in the Upper Tennessee. 



In the uppermost Tennessee drainage, Obovaria subrotunda is 

 extremely rare ; above Knoxville, it does not go anywhere into the 



