51. Shell with broken green rays; posterior ridge developed, with a radial dc' 



pression before and behind; Ohio, Cumberland and Tennessee Rivers 

 Cy progenia stegaria (Raf.) Fan Shell 

 Cyprogenia irrorata (Lea) 

 Shell scarcely rayed; posterior ridge low, with a radial depression be 

 hind 52. 



52. Umbonal markings fine; nacre white or pinkish 53. 

 Umbonal markings coarse; nacre purplish 54. 



53. Epidermis greenish; dorsal margin almost straight; Mississippi drainage 



^uadrula pustulosa (Lea) Pimplcback 

 Epidermis reddish-brown; dorsal margin curved; Ohio, Cumberland and 

 Tennessee Rivers 



^uadruld striata (Raf.) 

 Plethohasus cooperianus (Lea) 



54. Pustules scattered irregularly; beaks anterior; Mississippi drainage 



^uadrula tuherculata (Raf.) Purple Pimple-back 

 Cydonaias tuherculata (Raf.) 

 Pustules in 2;igzag lines; beaks central; Georgia 

 S^uadrula securiforrms (Conrad) 



55. With a long projection from the interdentum of one valve which iits into 



a depression in the interdentum of the other; shell lengthened, slightly 

 winged posteriorly; generally distributed, except for the Atlantic and 

 Pacific states 



Lasmigona viridis (Raf.) 



Lasmigona compressa (Lea) 

 Not so 56. 



56. Shell winged posteriorly, moderately full to flat, usually not much longer 



than high 57. 



Not so 60. 



57. Valves moderately full; nacre purple; south-central states 



Proptera purpurata (Lamarck) Purply 

 Shell flattened 58. 



58. With a low wing anteriorly; epidermis polished, usually rayless; shell 



gaping posteriorly; nacre purplish; Ohio and Mississippi valleys; New 

 York to Texas 



Proptera laevissima (Lea) Smooth Heel-splitter 



Leptodea laevissima (Lea) 

 Little or no wing anteriorly; epidermis rayed (with color markings) or 

 with many growth lines; not usually gaping; nacre similar or not 59. 



59. Epidermis green or dark; nacre pink, salmon or purple; cardinal teeth 



sharp-edged; Mississippi and St. Lawrence drainage 



Proptera alata (Say) Pink Heel-splitter 

 Epidermis yellowish; nacre silvery, often pink-tinted; cardinal teeth small 

 and dull; widely distributed, not reaching the far western states 



Lampsilis jragilis (Raf.) Fragile Paper Shell 



Leptodea fragilis (Raf.) 



155 



