78. Shell oval; epidermis somewhat polished, with faint rays (color mark' 



ings) ; Mississippi River 



Lampsilis higginsii (Lea) Higgin's Eye 

 Shell more triangular; epidermis somewhat cloth'like or satiny, with ob' 

 scure or no rays 79. 



79. No radial swelling or depression before the posterior ridge; Tennessee 



drainage 



^uadrula dollahelloides (Lea) 

 Lexingtonia dolahelloides (Lea) 

 With radial swelling or depression before the posterior ridge 80. 



80. Beak cavities narrowed up under the hinge line 8L 

 Beak cavities rounded, moderate to shallow 82. 



81. Posterior base distinctly drawn out to a blunt point; central states 



§^uadrula ohliquata (Raf.) 

 Pleurohema cordatum pyramidatum (Lea) 

 Posterior base more rounded; central states 



^uadrula cordata (Raf.) Ohio Pig-toe 

 Pleurohema cordatum (Raf.) 

 (Pleurohema ohliquum (Lamarck)) 



82. Epidermis almost smooth; south'Central states 



Ohovaria curta (Lea) 

 Pleurohema curta (Lea) 

 Epidermis in coarse, concentric folds; east'Central states 

 Pleurohema detectum (Frierson) 

 Plethohasus cicatricosus (Say) 



83. Shell almost two times as long as high 84. 

 Shell shorter 98. 



84. Shining yellow, rayless; Mississippi drainage and Gulf states 



Lampsilis teres (Raf.) Yellow or Slough Sand Shell 

 Lampsilis anodontoides (Lea) 

 Dark or with rays (color markings) 85. 



85. Epidermis dull to dark; faint rays, if present, confined to the posterior 



slope 86. 



Epidermis shining or with rays - 90. 



86. Beak cavity shallow; with a moderate posterior ridge; fairly large shells 



90. 

 Beak cavity moderate; no posterior ridge; usually small shells 87. 



87. Umbonal markings fine or inconspicuous; rays sometimes present on the 



posterior slope 88. 



Umbonal markings coarse irregular bars; usually rayless 89. 



88. Posterior margin slightly winged; beak markings many fine double loops; 



nacre bluish- white; Mississippi drainage 

 Lampsilis suhrostrata (Say) 

 Ligumia suhrostrata (Say) 

 Posterior margin not winged; no evident beak markings; nacre often 

 salmon to purple; central and lower Mississippi drainage 

 Lampsilis Uenosa (Conrad) Black Bean 

 M^cromya lienosa (Conrad) 



158 



