262 THE AMERICAN MIDLAND NATURALIST 



Seal Brown ■. - 20% 



Buffy Citrine 10% 



Aniline Black 10% 



Distribution in L- Erie^ — Localities. 



La Plaiiance Presque 



Bay Isle 



Warm Blackish Brown 50% 



Cinnamon Brown 50% - 



Buffy Citrine --50% 25% 



Seal Brown 25 % 



Deductions from Tables of Percentages and PI. HI. 



Again we find that the shells of L. Erie have lighter browns and 

 greater percentages of yellow. 

 In the Upper Ohio Drainage 



The darkening of both primary and secondary colors, (Yellowish 

 Olive and light browns to Brownish Olive and dark browns) is 

 observed descending stream in the Allegheny Shenango, Mahoning 

 Rivers and French Creek. In many cases the darkening in second- 

 ary colors can only be traced from tributaries to rivers. Some 

 characteristic primary stream colors are olive in the Allegheny, 

 yellow or brownish olive in Crooked Creek, greenish or brownish 

 yellow in the Shenango, Yellowish Olive in the Mahoning. 



In L. Erie. 



The shells of La Plaisance Bay are brownish yellow; those of 

 Presque Isle are prevailingly blackish brown, like those of the 

 Tuscarawas River in the Upper Ohio Drainage. 



Rays of Epidermis. 



Simpson — "shell rayed when young." 27 of 247 shells were rayed, 

 persisting in some cases until the 14th year. In quality, these 

 were finest in the largest rivers, medium in the small rivers and 

 creeks, where they were also more abundant. Prevailing color was 

 Greenish Olive. 



Relation of Epidermal Color to Estimated Age of Animals. 



With age, shells become reddish brown in the Upper Ohio Drain- 

 age. Data concerning L. Erie shells is fragmentary, but as a rule 

 in both^, brownish, tawney, and greenish hues decrease with age. 

 Darkening occurs early, about the 4-5 year. Older shells are mostly 

 reddish brown. No color or group of colors seemed peculiar to any 

 given age. ^ 



