THE MOLLUSCA 



997 



in (112) Surface pustulose; no radial furrow above the posterior ridge; 

 unicolored or rayed, never painted as in Quadrula s.s. 



Section Theliderma Swainson. 



This section comprises three well-marked groups: first, that of the typical species, Quadrula 

 lachrympsa Lea (Fig. 1483), having a quadrate or rhomboid shell with a wide, shallow radial 

 furrow in front of the posterior ridge; second, that of Q. pustulosa Lea, with a rounded, quad- 

 rate shell 'with no radial furrow; third, two small species from Georgia and Florida, rounded- 

 rhomboid in shape, without the furrow and with the surface covered with zigzag corrugations. 

 Most of the species are found only in the Southern States, but the first two groups have repre- 

 sentatives ranging north to Michigan and Minnesota. 



FIG. 1483. 



112(109) Surface smooth Section Fusconaia Simpson. 



While the majority of the species of this 

 section are found in the Southern States, it is 

 well represented as far north as Michigan and 

 the upper Mississippi. Type, Quadrula un- 

 data Bar. (Fig. 1484). 



FIG. 1484. 



