298 ORTMANN— CORRELATION OF SHAPE AND 



I have also a very interesting series from the Beaver drainage. 

 Just below the mouth of Beaver River, in the Ohio at Industry, pure 

 catillus is present with the average diameter of 57 per cent. 



Loc. No. 



Beaver River. 

 Wampum 14 



Mahoning River. 



Mahoningtown 3 



Coverts i 



Leavittsburgh 3 



Newton Falls i 



Shenango River (follows Wampum). 



Harbor Bridge 3 



Pulaski 5 



Sharpsville i 



Clarksville 9 



Shenango 5 



Jamestown 17 48 27 43 cocc. 



The elevation of the diameter at Clarksville is due to the pres- 

 ence of a number of quite young specimens. We have learned, 

 under the group of Fusconaia subrotunda, that the diameter of 

 young shells is comparatively greater. Older individuals at this 

 locality are all pure cocc'meiim. 



Even in a small creek like the NesJiannock, the law becomes 

 visible. 



Loc. ' No. Max. Min. Av. 



Eastbrook 8 43 36 40 cocc. 



Neshannock Falls 3 48 35 41 cocc. 



Volant 4 42 39 40 cocc. 



Leesburg 4 40 36 38 cocc. 



Similar conditions prevail in the Monongahela drainage. At 

 Charleroi, the form catillus is rather pure. From farther up I have 

 only scanty material, but at the mouth of Cheat River, at Cheat 

 Haven, catillus is present (diameter about 50 per cent, or slightly 

 more). From the West Fork River I have only specimens of 

 typical coccinewm, all with the diameter below 50 per cent. 



