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 w'rinkled 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, hut 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. 1 — 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 neaidy 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 tlie precise angle subtended 
