222 THE AMERICAN MIDLAND NATURALIST 



In the upper Ohio Drainage: 



As a general thing the colors are Hghter in the rivers than in the 

 tributaries. This species is exceedingly variable with regard to 

 nacre color. A general tendency to lighten in color may be observed 

 coming down the Allegheny thus confirming Wilson and Clark's 

 and Utterback's observations. It is true, however that at certain 

 stations it appears to darken, but this result is from a small num- 

 ber of shells. Such apparently also occurs in French Creek, but the 

 shells of the Allegheny are lighter than those of French Creek at the 

 nearest collecting point. Pearl blue is largely limited to the Al- 

 legheny River and its tributaries. Nacreous colors, are lighter in the 

 Monogahela than in its tributary, the Cheat. They also tend to 

 lighten in the Ohio River, but in the Shenango at the headwaters 

 they are deep vinaceous, (reddish purple), in hue, lower down 

 becoming more purplish. Characteristic Stream Colors appear to be, 



Purple drab for Potato Cr. 



Light Purple Drab for Sandy Cr. 



Vinaceous colors for Cheat River. 



Light Vinaceous Purple drab in Neshannock Cr. 



Light reddish to light purples in the Mahoning, lower down 

 becoming purplish lilac to slate purple. 



Vinaceous Gray is characteristic of the Ohio. 

 In Lake Erie: 



Presque Isle stands out for its large amount of reddish purple 

 shades, while La Plaisance Bay has grayish purple ones. The great 

 variability of Presque Isle shells may again be noted. Those from 

 other L. Erie localities than those given in L. Erie are so small that 

 percentages are not given. 



In Chautauqua Lake the shells appear to be mainly white. 



Observation on Sex Correlative Coloration, etc. {ij shells). 

 More males have a pearl blue nacre than females. They also 

 have a larger percentage of lilac shades. Females seem to be 

 characterized by a deeper purple color, and a greater number ot 

 lilac shades. 



4. — Pleurobema obliqutim coccineuni 



SIMPSON RIDGEWAY 



Rose-Pink Pale Vinaceous Pink, Light Ochraceous 



Salmon, Orange Pink. 

 Whitish-red* Pearl Blue, Venetian Pink, Light Pearl Blue, Burn Bl'ie 



* Pure whites appear to be negligible among the shells I examined. 



