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. 
Wehaohoibioal} | (Gaasgonancoud aoc cao.o 25 52 41 44 kirtl. (subrot.) 
Shenango River. 
lnteyrnore Jbinclxee GuagnocuenodoDoos 13 47 36 40 kirtl. 
Pislashsiteecsacamretictec bovis eect eters 18 49 40 44 kirtl. 
Shharnswalle pisces seo cunsictcuw sents 4 48 35 43 kirtl. 
Clarksville ties male aise cee et 18 50 36 45 kirtl. 
Pymatuning Creek (mouth) ..... I 30 30 39 kirtl. 
Mahoning River (follows Wampum). 
Nialvonin tow weer cei see 51 52 37 44 kirtl. (subrot.) 
@OVERES tr eh cad onsieiecmicspenien 6 47 40 43 kirtl. 
EVdinib ingyen eiciciieetevsers.cere 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 
