CONCHOLOGIA CESTRICA. /I 



Sub-genus MENETUS, H. and A. ADAMS, 1853. 



Shell, depressed; whorls rapidly increasing; periphery 

 angulated. 



M. exacutus, SAY. 



Planorbis exacutus, Say, Jour. Acad. Phila. F. S., II., 

 1821. 



M. exacutus. [W. G. B.j M. exacutus (abnormal). 



Fig, 141, Fig, 142, 



Shell, small, depressed ; whorls 4, wider than long, 

 carinated on the circumference ; umbilicus broad, and 

 deep ; aperture below the carina, and angulated by it. 

 H. iy 2t W. 4, mill. 



Station, ponds. Pickering Creek, Chester County. 



Sub-genus GYRAULUS, AGASSIZ, 1837. 



Shell, orbicular above, flat beneath ; whorls few, 

 rapidly increasing. 



G. deflectus, SAY. 



Planorbis deflectus, Say, Long's Exped, G ' [ * ef % c % 1 *' 



II., 1824. Fig, 143, 



Shell, small, depressed ; whorls nearly 5, 

 flattened, smooth, fine striate ; margin ob- 

 tusely carinate; last whorl deflected down- 

 wards near the aperture ; which is large and 

 very oblique. H. 2, W. 6, mill. 



Station, ponds and rivulets. Pickering Creek, Ches- 

 ter County ; frequent. 



