296 KANSAS UNIVERSITY SCIENCE BULLETIN. 



gin rather squarely rounded ; ventral margin gently bowed, 

 slightly emarginate and produced in females; posterior mar- 

 gin bluntly pointed, decidedly dorsally in female, sharply 

 pointed in male ; dorsal margin straight, very slightly ob- 

 lique, meeting the posterior at an angle of from 150 to 165 

 degrees. Umboidal ratio, near 0.20. Umbones rather low, 

 directed slightly forward, and heavily marked with a series 

 of broad, slightly curved A-shaped ridges, eight to ten in 

 number. Epidermis marked with numerous fine continuous 

 lines of growth, from light brown to dark, rusty brown, the 

 lighter specimens rayed posteriorly with broad bauds of green. 

 Ligament light brown, rather long, thin. 



Interior : Pseudocardinals double in the left, single and 

 sometimes double in the right valve, variable, generally thin 

 and lamellar, but occasionally pyramidal ; erect, finely ser- 

 rate, left anterior generally twice as long as the left posterior 

 and set on a diagonal parallel to it. Lateral teeth long, thin, 

 slightly curved. Anterior adductor cicatrix well excavated, 

 much longer than wide ; retractor cicatrix large and well im- 

 pressed. Posterior cicatrices variable, large, lightly im- 

 pressed, confluent. Dorsal muscle scars from one to six, 

 variable in position. Pallial line faint posteriorly but well 

 marked anteriorly. Cavity of beaks shallow, of the shell 

 rather large. Nacre white with considerable iridescence. 



L. subrostrata is found in eastern Texas and as far north as 

 latitude 41 degrees in the Mississippi drainage. In Kansas it 

 is found in all the drainage basins and is fairly common in all 

 of them. The species has been reported as far west as Ellis 

 (Call). Subrostrata is a lover of mud beds and quiet waters. 

 It occurs in permanent ponds and lakes as well as streams. 

 In the southern drainage, while quite common in the quiet 

 streams which flow into the larger rivers, it is not common 

 in the rivers themselves. The very characteristic pointed 



* Umbones too worn to determine accurately. 



