Genus Lastena Rafinesque. 

 Genus Gonidea Conrad. 

 Genus AnodontoidES Simpson. 

 Genus Pegias Simpson. 

 Genus Arcidens Simpson. 

 • Genus SymphynoTa Lea. 

 Subgenus SymphynoTa Lea. 



1. Group of Symphynota compressa. 

 Subgenus Lasmigona Rafinesque. 



2. Group of Symphynota costata. 

 Subgenus Fterosygna Rafinesque. 



3. Group of Symphynota coinplanata. 

 Genus Alasmidonta Say. 

 Subgenus Alasmidonta Say. 



1. Group of Alasmidonta iiiididata. 

 Subgenus Pressodonta Simpson. 



2. Group of Alasmidonta calceola. 



3. " " " heterodon. 



4. " " " collina. 



5. " " " holstonia. 

 Subgenus Rugieera Simpson. 



6. Group of Alasmidonta marginata. 

 Subgenus Buti^ELLA Simpson. 



7. Group of Alasmidonta arctda. 



Genus Hemilastena Agassiz. 

 Genus Margaritina Schumacher. 



