220 THE AMERICAN MIDLAND NATURALIST 



Distribution in Lake Erie — Localities. 



Presque Isle Cedar La Plaisance 



Bay Point Bay 



Pearl Blue and allied colors 57%-- ioo% 20% 



Pale Ver. Violet and allied colors 37% 



Light Pink. Viol, and allied colors 80% 



Pale Salmon and allied colors 6%.... 



Deductions from Tables of Percentages and Plate III. 



Pearl blue is most largely represented in Lake Erie. Colors in 

 the Upper Ohio tend to be grayish in nature, those corresponding 

 in L. Erie, more of a violet. 

 In the Upper Ohio Drainage: 



Pearl blue is more prominent in the Allegheny River than in its 

 tributaries, and is more abundant in the Beaver than in the 

 Allegheny. The nacreous color apparently tends to acquire deeper 

 tones in the lower stretches of both the Allegheny and the Shenago. 

 Altho' pearl blue is recorded at its lowest station, grayish lavender 

 would be a composite shade characterizing shells from French 

 Creek, where the pale verbena violet of the upper stretches fades to 

 pearl blue lower down. A similar fading is seen in the Shenango, 

 whose shells are more of a blue compared with its sister river, the 

 Mahoning, where they tend to take on a lilac tinge. Perhaps shells 

 really coming from the Mahoning were the ones of this species 

 obtained in the Beaver River. In Slippery Rock Creek, the shells 

 are pearl blue, in the Ohio River, pale grayish vinaceous. 

 In Lake Erie: 



A bluish violet color characterizes the shells obtained at Cedar 

 Point. This shade accompanied by pinkish violet is distinctive for 

 Presque Isle, while pinkish violets are in the great majority at La 

 Plaisance Bay. Examination of PI. Ill shows more fully the 

 variability at Presque Isle. 



Observation on Sex Correlative Coloration as Associated with Nacreous 



Cohr. {iQ shells). 

 Females appear to be prevailingly pearl blue, while the males are 

 characterized by pale vinaceous colors. The amount of grayish 

 lavender represented is equivalent in both. 



3. — Elliptio dilatatus 



SIMPSON RIDGEWAY 



Deep purple. Light Vinaceous Lilac, Light Vinaceous 



Purple, Deep Vinaceous, Deep Vinaceous 



