362 KANSAS UNIVERSITY SCIENCE BULLETIN. 



semicircular in outline and quite deep, rather small when 

 compared to the size of the shell ; posterior scars distinct, 

 well impressed, the adductor cicatrix quite elongate. Dorsal 

 muscle scars small pits scattered on the lower surface of the 

 interdentum. Cavity of the shell not large, of the umbones 

 small. Nacre white or salmon-pink. 



Q. coccinea is found throughout the Mississippi and St. 

 Lawrence drainage basins. It is common to all the Kansas 

 river systems. I have never found it abundant, although 

 it is generally present in all streams of any size. It is 

 rare in the Wakarusa river at Lawrence and absent from the 

 Kansas river there. 



The variation is mainly in the color of the epidermis and 

 the thickness of the shell. The shells from the clear- water 

 rivers of the southern drainage are heavier than those from 

 the Kansas and Marais des Cygnes. The nacre of coccinea is 

 either pink or white. The white form is the commoner one. 



This species is often confused with Q. rubiginosa. Ruhigi- 

 nosa is more sharply and distinctly biangulate and produced 

 posteriorly than is coccinea. The posterior portion of the 

 ventral margin of Q. coccinea is slightly rounded, that of Q. 

 rvhiginosa is emarginate. Q. trigona is distinguished from 

 Q. coccinea by its much inflated beaks. 



Quadrula solida Lea. Plate LXXXV. 



Unio solidus Lea, Trans. Amer. Phil. Soc, vi, 1838, p. 13, pi. v, fig. 13. 

 JJnio fulgidus Lea, Proc. Amer. Phil. Soc, iv, 1845, p. 164. 



Shell moderate to large in size, very thick and solid, par- 

 ticularly in region of the beaks, roundly quadrate or trian- 

 gular, subinflated. Anterior margin flattened above, rather 

 abruptly rounded below ; ventral margin almost straight, 

 slightly incurved centrally. Posterior margin straight or 

 curved, sometimes slightly incurved centrally, a little pro- 

 duced ventrally ; dorsal margin more or less oblique, 

 straight or curved, sometimes forming one unbroken curve 



