VARIATION IN EPIDERMAIv COLOR OF NAJADES. 273 



Olive Ochre 20% 



Brownish Olive ': ...' ._ 20% 



Carob Brown 20% 



Bister 10% 



Dark Greenish Olive 10% 



Distribution of Colors in L. Erie — Localities. 



Cedar Point Presque Isle 



Chestnut - _ 33% 16% 



Olive Ochre 33% 33% 



Brownish Olive 16% 16% 



Carob Brown..... 16% 16% 



Bister 16% 



Deductions from Tables of Percentages, etc. 



Browns are in excess in the Upper Ohio as compared with L. 

 Erie. Olives and golden yellow hues are peculiar to L. Erie. 



In the Upper Ohio Drainage 



For a great part of the Allegheny's course a darkening may be 

 seen in the primary color from greenish to olive and brownish colors. 

 The series from French Creek and the Ohio apparently do not 

 conform to the general rule. Alore positive evidence can only be 

 secured with a larger number of shells. Dark Citrine could be 

 termed a characteristic primary color for the Ohio, Yellowish 

 Citrine for French Creek. We may note at any rate, that the darker 

 colors are more abundant in the tributaries than in the rivers and 

 vice-versa, while browns are more abundant in the Ohio than in the 

 Allegheny. 



In LaJ?e Erie 



Browns are most numerous at Cedar Point, while Presque Isle 

 has the larger proportions of black colors. 



Rays of Epidermis 



6 of 54 shells showed raying persisting until the 15th year. 

 They were coarse in the specimens examined and appeared only 

 in those from rivers. Their color was Greenish Olive, and the 

 oldest age to which they persisted was 16 years. 



Relation of Epidermal Color to Estimated Age of Animals. 



Juveniles of this species are mostly green. Darkening may occur 

 as early as 7 years and is complete at 14. No color or group of 

 colors seems peculiar to any given age. 



