256 THE AMERICAN MIDLAND NATURALIST 



Dresden 20% 25% 



Ecru Olive 25 % 25 % 25 % 



Tawney Olive. _ 15% 50% 25% 



Deductions from Tables of Percentages and PI. III. 



Yellowish greens are more abundant in L. Erie than in the 

 Upper Ohio Drainage ; the browns of L. Erie are of a reddish variety, 

 those of the Upper Ohio darker, towards black. Generally, the 

 shells of Iv. Erie are seen to be lighter in color. 

 In the Upper Ohio Drainage. 



With few exceptions, the color of the epidermis is darker in the 

 rivers than in their tributaries, and darker at the lower stations of 

 the latter than at the upper. This applies to both primary and 

 secondary colors. At Crooked Creek, Creekside, the primary color 

 is a sort of Greenish Olive, but lower down at Rosston, this is 

 succeeded by a darker Yellowish Olive. The secondary colors 

 has deepened to a Seal Brown, acquiring at a near station on the 

 Allegheny, Kelley, a Cinnamon Brown, while the primary color 

 has deepened to a Brownish Olive.* The same type of change 

 may be traced down the latter stream, as well as from the tributaries 

 of the Monongahela, Dunkard and 10 mi. Creeks to that body of 

 water. As the Ohio River is approached, epidermal color becomes 

 darker and darker. Some characteristic primary colors of streams 

 are Brownish Olive for the Allegheny ; Greenish Olive for Crooked 

 Creek. 

 In L. Erie. 



The shells at Presque Isle have less Yellowish Green than those 

 at La Plaisance Bay. Cedar Point is characterized by a large 

 percentage of Tawney Olive colors, while the . Maumee River 

 draining into L. Erie has an excessive proportion of brown among 

 its shells. In this as well as in other species, different parts of the 

 same collecting locality, such as the various parts of Presque Isle 

 Bay, are apt to show a peculiarly distinctive epidermal color. 

 Rays of Epidermis. 



According to Simpson, this shell is faintly rayed in the young 

 state. 29 of 275 shells had rays, mostly medium in size. My ob- 

 servations indicated that they persisted in some until the nth 

 year. Raying was most abundant in specimens from the small 

 rivers and creeks, rather than in the larger rivers and lakes. Their 

 prevailing colors were olive, yellowish or darker green. 



* Names of Ridgeway Colors are capitalized in this paper. 



