CONCHOLOGIA CESTRICA. Va 
P. armigera, SAY. 
Planorbis armigerus, Say, Jour. Acad. Phila. F. S., 
LU Agsek 
Shell, light brown, polished; whorls 4, P. armigera. 
sub-cylindrical, and sub-carinate below ; um- hea = 
bilicus wide, and deep; aperture rounded, (om) 
with six white teeth, far within the throat; 
the largest thin, oblique, running back from Aperture of 
the left to the right side; on the left of this a Fie. 148, 
is a small one, and around the vault four 
others; the teeth sometimes wanting. H. Pp) 
2%, W. 6%, mill. 
Station, Schuylkill River, and tributaries. Chester 
County. 
Genus ANCYLUS, GeEorFFroy, 1767. 
Shell, thin, patelliform, non-spiral; apex di- Animat of 
Ancylus. 
rected to the right; aperture wide; peritreme [w.cG. B.| 
continuous, simple, entire. zieyiee: 
Animal, tentacles triangular; mantle in- 
cluded; pulmonary orifice protected by a 
branchial appendage ; foot large. = 
A. rivularisy Say, Jour. Acad. Bhila, PF. -S., I1., 
1817. 
Shell, delicate, depressed-conic ; apex ob- 4. rivularis. 
tuse nearer to, and leaning towards, one eae. 
side, and one end; aperture oval, narrower 
at one end, entire; within milk white. H. = 
1%, W. 3, mill. 
Station, cn dead shells, and stones, in streams. Ches- 
ter County; frequent. 
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