370 KANSAS UNIVERSITY SCIENCE BULLETIN. 



II. Shell Smooth. 



D. Laterals and pseudocardinals present, 

 b. Shell noD-alate. 



2. Shell solid, compressed, beaks low and compressed, psendocardinals 



fairly heavy, interdentum present and prominent. 



a. Shell roundly triangular in outline. 



a'. Shell, with broad, green rays, incurved ventral margin 

 and lateral furrow. Vy progenia alberti, 



b". Shell without lateral furrow, ventral margin not in- 

 curved. Plagiola securis. 



b. Shell elongately ellipsoid in outline. 



a'. Shell broadly or narrowly ellipsoidal ; epidermis light 

 to dark brown, with fine hair rays posteriorly ; beaks 

 with very fine crenulations. Groups of Phychobrunchiis 

 phascolus . 



b'. Shell generally narrowly elliptical; epidermis dark 

 brown or black, eradiate; beak sculpture a few very 

 coarse concentric folds ; nacre white, pink, or purple. 

 Vnio gibbosus. 



c. Shell quadrate, sometimes with green rays over the ambones. 



Quadrula rubiginosa, 



3. Shell roundly elliptical, triangular or quadrate, inflated in the umboidal 



region or just posterior to it, solid, pseudocardinals heavy and rag- 

 ged, the right pseudocardinal surrounded by a trench. 



a. Shell fairly solid, roundly triangular or quadrate, beaks not 

 high. Group of Quadrula trigona. 



b. Shell solid, roundly elliptical, beaks not high. 



a'. Beaks full but not high; epidermis honey-brown with 

 sometimes a greenish cast. Obovaria ellipsis. 



h^. Beaks rather compressed ; epidermis very dark brown 

 or black. Quadrula ebcnus. 



c. Shell roundly triangular, high, with full, high, rounded, in- 



curved beaks, very solid, with very large pseudocardinals. 

 Group of Quadrula plena, 



d. Shell suborbicular, heavy, large, with rather full, high beaks, 



Quadrula houstonensis. (This will also include the smooth, 

 circular forms of Q. pustulosa.) 



§This is intended as check on the forms of L. gracilis which have lost their alee. 



