CONCHOLOGIA CESTRICA. 



95 



Shell, large, thick, oblique, sub-rhomboid, ventricose ; 

 beaks prominent, undulated ; epidermis dark-brown, or 

 yellowish, without rays; surface undulated, smooth; the 

 anterior half of the valves, near their edge, thickened 

 internally. H. 3, W. 5.5, T. 2.3, inches. 



Station, Schuylkill River, Chester County. 



A. edentula, SAY. 



Alasmodonta edentula, Say, New Harm. Dis., II., 1829. 



A. edentula, 



Fig, 194, 



Shell, transverse-oval, compressed, olivaceous, rayed 

 with green ; beaks small, undulated ; within bluish- 

 white ; teeth obsolete, but the peculiar curvature, be- 

 neath the beaks, shows their locality. H. 1.5, W. 2.75, 

 T. .8, inches. 



Station, running streams. Brandywine Creek, Ches- 

 ter County; common. 



A. Tryonii, LEA, Jour. Acad. Phila. N. S., VI., 1862. 



A. Tryonii, 



Fig, 195, 



