44 



Bryant Walker 



Section OUADRULA s. s. 



Shell quadrate or rhomboid; surface pustulous, with a high, rounded 

 or sharp posterior ridge, above which on the posterior slope is a decided 



Fig. 144 



I^ig- 145 



radial furrow; umbonal region high; epidermis shining, usually painted 

 with a beautiful pattern of triangular spots or chevron-shaped lines. 



Type: Unio cylindricus Say, fig. 144. Animal, Q. metanevra Raf., fig. 145. 



Section THELIDERMA (Swainson, 1840) Simpson. 



Fig. 146 



Shell rounded, quadrate to rhomboid, solid, pustulous ; beaks rather 

 prominent, sculpture consisting of a few, rather coarse, subparallel ridges; 

 anterior end rounded, base often arcuate, posterior end truncate, high and 

 angled behind the ligament, epidermis rarely rayed, never as in Quadrula s. s. 



Type: Unio lachrymosus Lea, fig. 146. 



