276 ORTMANN— CORRELATION OF SHAPE AND 



Pennsylvania. This is formed by two main branches, Shenango 

 and Mahoning, which unite below Newcastle, at Mahoningtown. I 

 shall begin with the only locality in the Beaver proper, then go up 

 the Shenango to the mouth of Pymatuning Creek, and finally go up 

 the Mahoning. 



Loc. No. Max. Min. Av. 



Beaver River. 



Wampum 25 52 41 44 kirtl. (subrot.) 



Shenango River. 



Harbor Bridge 13 47 36 40 kirtl. 



Pulaski 18 49 40 44 kirtl. 



Sharpsville 4 48 35 43 kirtl. 



Clarksville 18 50 36 45 kirtl. 



Pymatuning Creek (mouth) i 39 39 39 kirtl. 



Mahoning River (follows Wampum). 



Mahoningtown 51 52 37 44 kirtl. (subrot.) 



Coverts 6 47 40 43 kirtl. 



Edinburg 4 42 39 40 kirtl. 



In the Ohio, just below the mouth of the Beaver (at Industry), 

 the diameter is 47 per cent. Thus the Beaver-shells are clearly less 

 swollen. While all these specimens are rather uniform in diameter, 

 it is seen that the lowest average is farthest upstream. Specimens 

 with over 50 per cent, are found frequently only at the lowermost 

 stations (Wampum and Manoningtown), and specimens with lowest 

 diameter (below 40 per cent.) are most frequent farther up. The 

 very high average at Clarksville (45 per cent.) is due to an unusual 

 number of young specimens, which, as we have seen, tend to elevate 

 the average ; and the low average at Harbor Bridge is due to the 

 fact that mostly large specimens are among them, which depress the 

 figures. 



It should be mentioned that the type-locality for kirtlandiana is 

 in the " Mahoning River, Ohio," that is to say, farther up than any 

 of my localities, and that the diameter as given by Lea's illustra- 

 tion is 44 per cent. 



Thus nearly all of the shells from the Beaver drainage fall 

 under kirtlandiana. 



Finally, I have shells belonging here from the Monongahela 

 drainage. At present, the Monongahela in Pennsylvania and parts 



