64 



Eleventh Genus CYCLAS. 



Two muscular impressions; lamellar teeth 

 oblique ; wrinkles zonal ; contour not thickened. 



This genus should be reformed, notwithstand- 

 ing the labours of MEGERLE and FERUSSAC. I 

 propose to divide it into four sub-genera, which 

 may perhaps form as many genera. 



1st. Polymesoda. Many intermediary teeth 

 on both valves ; shell rounded or somewhat trans- 

 versal. Type Cyclas caroliniana, Bosc, &c. 



2d. Phymesoda. One intermediary tooth in one 

 valve ; shell somewhat transversal. Type Cyclas 

 lacustris C. dubia, SAY, &c. 



3d. Amesoda. No intermediary tooth in one 

 valve, at least; shell slightly transversal. Type 

 Cyclas similis, SAY. C. lasmampsis, <$fc. 



4th. Corbicula (MEGERLE.) Many interme- 

 diary teeth in both valves ; shell triangular, 

 somewhat lengthened. Type Cyclas hammalis, 

 C. fluviatilis, &c. 



SPECIES LXII. Cyclas lasmampsis (Amesoda 

 lasmampsis.} 



Shell translucent, ventricose, slightly rounded ; 

 wrinkles close together, unequal, more distant 

 and broad superiorly ; lamellar teeth flexuous, the 



