264 THE AMERICAN MIDLAND NATURALIST 



Prouts Brown 25% 



Mummy Brown 25% 



Deductions from Tables of Percentages and PL III. 



Light colors, (Buffy Olive), are apparently equivalent in the 

 Upper Ohio Drainage and L. Erie, but the browns are deeper hued 

 in the latter, much as in the preceding species. 

 In the Upper Ohio Drainage. 



Shells from the rivers are darker than those from the tributaries. 

 A partially incomplete series of darkening primary and secondary 

 colors may be traced descending the Allegheny, Shenango, and 

 Mahoning Rivers. This would be more complete had more material 

 been available. Characteristic primary colors are Buffy ones for 

 the Allegheny, Citrine for the Shenango. Due again to lack of 

 material, there is no outstanding differences between the shells 

 of the Monongahela and its Tributaries. Darkening of the epidermis 

 occurs descending the Ohio. 



In L. Erie 



Presque Isle shells are distinguished from those of La Plaisance 

 Bay by the abundance of browns, and the practical absence of 

 yellow colors. 



Rays of Epidermis 



Simpson — "often rayed." 3 of 68 shells showed raying, in shells 

 9-12 years of age, and persisting at least until that age. The 

 prevailing color of rays was greenish olive. 



Relation of Epidermal Color to Estimated Age of Animal. 



With age, the Chestnut or dark colors become in the majority. 

 Darkening may occur as early as the 7-9 year, and seems complete 

 at 15. "Greenish" is always a. minority color. Darkening occurs 

 less rapidly in L. Erie, and the percentage of yellows apparently 

 increases with age in the Upper Ohio Drainage. Young shells were 

 not plentiful among my material. 



Observation on Sex-Correlative Coloration as Associated itith Epider- 

 mal Color (6 shells). 



Within the limits of the small number of shells considered, the 

 males stand out for blackish colors with age, and Buffy Olives in 

 youth. Females had lighter browns than males, and young speci- 

 mens were Brownish Olives. 



