^uadrula argentea (Lea) 

 Pleurohema oviforme argenteum (Lea) 



107. Shell triangular or wedgC'shaped, often with many fine radial lines on 



a flattened posterior slope; epidermis usually semi'shining, with rays 

 broken, spotted or wavy 108. 



Shell ovate; posterior slope usually rounded and without many fine 

 radial lines; epidermis usually polished, with rays complete, sometimes 

 wavy 118. 



108. Lateral teeth scarcely longer than the lateraMike cardinals; shell thin 



and usually rayless; becoming about five and onchalf inches long; 

 Ohio River drainage 



Lampsilis ovata (Say) Ohio Pocketbook, Grandma 

 Lateral teeth distinctly longer than, and unlike, the cardinals; usually 

 rayed and smaller 109. 



109. Shell much flattened; hinge plate very heavy; epidermis yellow, with 



dark rays which may be broken up into square blotches; central and 

 east-central states 



Plagiola hneolata (Raf.) Butterfly Shell 

 Shell moderately swollen 110. 



110. Posterior ridge obscure or faintly double; rays usually wavy 111. 

 Posterior ridge well developed 114. 



111. Hinge teeth heavy; muscle scars small and round 112. 

 Hinge teeth moderate; muscle scars large 113. 



112. Beaks small, median; rays usually wavy; Ohio River drainage 



Lemiox fahahs (Lea) 

 Micromya fahalis (Lea) 

 Beaks more anterior; rays obscure; Tennessee drainage 

 Lemiox rimosus (Raf.) 

 Micromya caehtus (Conrad) 



113. Nacre purplish; ventral margin almost straight; Ohio River drainage 



Dysnomia sulcata (Lea) Cat's Paw 

 Nacre white or salmon; ventral margin outcurved; Ohio Rjver drainage 

 Dysnomia personata (Say) 



114. Rays obscure; shell much swollen, with the dorsal and posterior maf 



gins meeting at an angle of about 90°; Tennessee and Cumberland 

 Rivers 



Dysnomia arcacformis (Lea) Sugar-spoon 

 Rays usually broken; shell full, with a sloping posterior-dorsal margin 



115. 



115. Posterior muscle scars very deep; posterior ridge of female toothed and 



much inflated; Tennessee 



Dysnomia hrevidens (Lea) 

 Posterior muscle scars shallow; posterior ridge of female not greatly 

 expanded 116. 



116. Lower half of posterior ridge rounded; lunule often very wide; central 



states 



Truncilla donaciformis (Lea) 



163 



