CONCHOLOGY. 109 



L. catascopium.* L. lapidaria.* 



L. columella.* L, dissimilis.* 



L. elongatus.* L. ponderosa.* 



L. reflexus.* L. Integra.* 



L. appressus.* L. porata.* 



L. elodes.* L. lustrica.* 



L. limosa.* L. grana.* 

 L. subglobosa.* 



2. Genus Phtjsa. PI. X. 



Anhnai. See Helix. 



Shell. General sinistral, oval, oblong, or globular, very smooth, 

 spire prominent, aperture oval, contracted posteriorly, right edge 

 sharp, columella twisting obliquely, and enlarging to join itself to 

 the anterior part of the margin, the whorls turning to the left 

 hand gives this shell the appellation of heterostrophe. Inhabit? 

 the ditches of America and Europe. Ten species. 



Physa fontinalis. Physa hypnorum. 



P. subopaca. 



P. castanea.* P. aurea.* 



P* decisa.* P. gyrina.* 



P. elongata.* P. heterostropha.* 



P. ancillaria.* 



3. Genus Planorbis. PI. X. 



Animal. See Helix. 



Shell. Discoid, spire depressed, or involuted almost in the 

 same vertical plane, causing the shell to be depressed on each 

 side, aperture oblong, luniform, axis remote, margin not reflected ; 

 no operculum. Inhabits the lakes of America and Europe. 

 Twenty-two species. 



Planorbis cornu-arietis. Planorbis orientalis. 



P. corneus. P. carinatus. 



P. spirorbis. P. lutescens. 



P. hispidus. P. nitidus. 



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