304 KANSAS UNIVERSITY SCIENCE BULLETIN. 



L. Iscvissima is distributed over the Mississippi drainage 

 generally, and from western New York and southern Michi- 

 gan to eastern Texas. In Kansas it is found in the Kan- 

 sas river and many of its tributaries, as far west as the 

 junction of the Solomon with the Smoky Hill river, in Dickin- 

 son county. It has also been reported from Fall river and 

 the Arkansas in the southern drainage. Its habitat is mud 

 or sand-banks, in quiet water of some depth. The delicate 

 character of the shell and the hinge render it unfit for other 

 conditions. 



This is one of the thinnest of the Unios. The most strik- 

 ing character of the shell is the peculiar similarity of the 

 pseudocardinals and laterals. When perfect, it is a beautiful 

 shell. The differences from other closely allied forms has 

 been noted under L. alata and L. gracilis. It is not a vari- 

 able species. 



Lampsilis leptodon Rafinesque. Not figured. 



Unio leptodon Rafinesque, Ann. Gen. Sci. Phys. Brux., 1820, p. 295, 



pi. LXXX. 



Symphynota tenuissima Lea, Trans. Amer. Phil. Soc, in, 1829, p. 453, 

 pi. XI, fig. 21. 



Shell small, thin, elongate ellipsoid, compressed, connate. 

 Anterior margin an abrupt curve ; ventral margin decidedly 

 bowed ; posterior margin elongately and roundly pointed ; 

 dorsal margin straight. Umboidal slopes very flatly rounded 

 — in fact, almost straight. Umbones placed well forward 

 ( umboidal ratio, about 0.18) . Umbones much flattened and 

 very small. Epidermis smooth and shining, greenish straw- 

 color, heavily radiate. Lines of growth dark and continuous, 

 but few in number. 



Interior : Pseudocardinals degenerate and hardly percepti- 

 ble in the left valve ; single, small, delicate and irregular in 

 the right valve. Lateral teeth long, straight, extremely 

 lamellar, sometimes single in both valves. Anterior ad- 

 ductor cicatrix well impressed, much longer than wide ; 



