Section Pi^ethobasus Simpson. 

 lo. Group of Pleurobema aesophus. 



TETRAGEN^. 



Genus Quadrula Rafinesque. 

 Section Crenodonta Schliiter. 



1. Group of Ouadrnla plicata. 



2. ' " " " trapezoides. 

 Section Quadrula Rafinescjue. 



3. Group of Qimdrula mctcmevra. 

 Section TheudERMA Svvainson. 



4. Group of Qiiadrula lachryiiwsa. 



5. " " " pustulosa. 



6. ■' " " infucata. 

 Section Fusconaia Simpson. 



7. Group of Quadrula headleiana. 



8. " " " trigona. 



9. " " " subrotunda. 



10. " " " glandacea. 



Section Pachynaias Crosse and Fischer. 



11. Group of Quadrula spheniopsis. 

 Subgenus Rotundaria Rafinesque. 



12. Group of Qyfidrula hiherculata. 



13. " " " ostreata. 



14. " " " percompressa. 



FAMILY MUTEUD^. 



Genus GivAbaris Gray. 

 Section Glabaris Gray. 



1. Group of Glabaris crispaius. 



2. " " " inaequivalvis. 



3. " " " trapesialis. 



4. " " " trigonus. 



Genus Mycetopoda d'Orbigny. 



