996 FRESH-WATER BIOLOGY 



109 (no) Surface plicate. . . . Section Crenodonta Schluter. 



The species of this group, characterized by the heavy, pHoite sculpture of the valves, are 

 among the largest and heaviest of the American Unionidae. They are very abundant throughout 

 the Southern States from Georgia to Texas. Two species range north into the St. Lawrence 

 drainage, the headwaters of the Mississippi, and to Lake Winnipeg. Type, Quadrula plicala 

 Say (Fig. i48i;Xi). 



Fig. 1481. 



no (in) Surface pustulose, with a radial furrow above the posterior ridge, 

 usually painted with triangular spots or chevron-shaped 

 hnes. - : ... Section Quadrula s.s. 



The typical species. Q- cylindrica Say (Fig. 1482; X i), ranges through the entire Ohio, 

 Cmnberland, and Tennessee river systems and west to Arkansas. A few other, less elongated, 

 species are found in Tennessee and Alabama. 



Fig. 1482. 



