2()0 THE AMERICAN MIDLAND NATURALIST 



Distribution in ly. Erie— Localities. 



La Plaisance Presque I. Chautaugua L. 



Chestnut Brown -. :.. 25% 25% 



Dresden Brown , 25 % 25 % 



Cinnamon Brown ...., -25% 25% 



Yellowish Citrine _ 50% 25%.' 25% 



Brownish Olive , ...25 % ....25% 



Deductions Jram Tables of Percentages and PL III. 



Iv. Erie is seen to contain more yellow shells than the Upper 

 Ohio Drainage, and its browns are of a lighter color. Black seems 

 to be in a minority in the Upper Ohio Drainage. 

 In the Upper Ohio Drainage. ' ■ 



Here we observe there is a greater percentage of dark colors in 

 the rivers than in the tributaries. A general darkening may be 

 observed descending the Allegheny — the primary color, originally 

 of an olive hue assuring brownish and buflfy hues, while the second- 

 ary colors pass from light reddish brown shades to dark ones. 

 A similar change may be observed in French Creek, the Shenango 

 and Mahoning Rivers. A characteristic stream color of the latter 

 is an olive shade; that of the Allegheny, a brown. For others 

 see the combinations of primary and secondary colors presented 

 presented on Pi. III. 



Buffy primary colors characterize the Allegheny, Brownish Olive 

 French Creek, Buffy Olive the Shenango, Olive the Mahoning. 

 In L. Erie. 



La Plaisance Bay alone is represented by yellow colors to an 

 appreciable amount, those of Presque Isle are prevailingly brown. 



Chautauqua Lake stands out for the absence there of vivid 

 reddish shades of brown. 



Rays of Epidermis 

 Simpson — "often faintly rayed in young specimens" — 32 of 

 509 shells were rayed. Rays may persist as late as the 14th year, 

 and were most abundant in specimens from small rivers and 

 creeks, were mostly medium in texture, and Greenish Olive was 

 their most common color. 



Relation of Epidermal Color to Estimated Age of Animal. 



Dull green is more plentiful in the young of Upper Ohio shells, 

 yellowish brown in those of L. Erie. Shells from the former darken 

 rapidly after the 6th year, in the latter about the 8th. The mature 



