258 THE AMERICAN MIDLAND NATURALIST 



Distribution of Colors as a Whole in L. Erie. 



Prouts Brown.- 30% 



Dull Citrine 20%. 



Yellowish Citrine 20% 



Mars Brown..... , 20% 



Yellowish Olive 10% 



Distribution in L. Erie — Localities. 



La Plaisance Cedar Presqiie 



Bay Point Isle 



Prouts Brown... .". 50% 



Dull Citrine ......25 % 25 % 25 % 



Yellowish Citrine 25% 25% 



Mars Brown :. ♦. 25% 



Yellowish Olive 50% 50% 



Deductions from Tables of Percentages and PI. III. 



Yellowish and greenish hues are most abundant in h- Erie, 

 showing that shells there have brighter colors. There are more 

 buffy or darker colors in the Upper Ohio Drainage, where reddish 

 browns are characteristic. 

 In the Upper Ohio Drainage. 



We observe from the above tables that the darker browns are 

 more abundant in the rivers, the lighter colors in the tributary 

 streams. Primary and secondary colors are observed to darken 

 descending the Allegheny, Shenango Rivers and French Creek. 

 Characteristic stream colors for this and most of the species of 

 shells dealt with are best given in PI. III. In the tributaries the 

 colors are usually greenish yellow hues. Characteristic stream colors 

 are yellowish green. (Citrine), in the Allegheny, greener shades 

 of Citrine in French Creek, buff varieties of this in the Shenango, 

 olive varieties in the Mahoning. At the nearest approach of these 

 streams to the Ohio the shells are found to blacken. 

 In L. Erie. 



Presque Isle shells have yellow colors, La Plaisance Bay, brown. 

 Those of Cedar Point are more of a Yellowish Olive. 



Rays of Epidermis. 

 Simpson reports no rays for this species. 4 of 107 shells were 

 rayed, persisting at least until the loth year. The rayed shells 

 were L. Erie specimens. The prevailing color was Greenish Olive. 



Relation of Epidermal Color to Estimated Age of Animal. 



Juvenile shells are mostly yellowish in the Upper Ohio, those 



