DESCRIPTIONS OF 



TERRESTRIAL SHELLS OF NORTH AMERICA. 



No. 1.— The Article « CONCHOLOGY," in Nicholson's Ency- 

 clopaedia, Am. Ed., anno 1818. 



1. Helix albolabris. — Shell thin, fragile ; convex, imperfo- 

 rated ; with six volutions, whorls obtusely wrinkled across, and 

 spirally striated with very fine impressed lines, a little waved by 

 passing over the wrinkles, both becoming extinct towards the 

 apex, which is perfectly smooth ; aperture lunated, not angulated 

 at the base of the column, but obtusely curved, lip contracting the 

 mouth abruptly, widely reflected, flat and white. 



Length of the column three-fifths of an inch ; breadth one inch. 



Plate 1, Fig. 1. Lister, Conch, tab. 47. ?•— Rhodia, Gmelin's 

 Ed. Syst. Nat. 



The common garden snail, frequenting moist shaded situations, 

 and is generally well known. It is very probable that this is the 

 Rhodia of authors, but as in the description of that species nothing 

 is mentioned of the reflected lip, and not having in our possession 

 the volume of Chemn. Conch, referred to for a figure of it, we have 

 made an interrogative reference, and for the present have adopted 

 a new name. 



2. H. ARBOREUS. — Shell very thin, fragile, depressed, horn 

 color, pellucid, very little convex : whorls four, irregularly wrinkled 

 across ; aperture sublunated, lip thin, brittle, junction with the 

 body whorl acute ; umbilicus large and deep. 



Length, one-tenth of an inch nearly; breadth nearly one-fifth. 



Plate 4, Fig. 4, 



Under the bark of decaying trees very common. Inhabitant 

 pellucid ; base white, acute behind, not extending forward before 

 the head ; head and neck dusky ; tentacula four ; lower ones very 

 short ; eyes placed in the tip of the superior pair. 



The application of the Goniometer, upon some commodious con- 

 struction, might very much facilitate the investigation and deter- 

 mination of species, by ascertaining the precise angle subtended 



