136 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



side cusp and inner lower lateral expansion of the base of attachment, and the 

 complete suppression of the cutting point to the inner side cusp. The marginals 

 have a sole-shaped base of attachment, and truly aculeate cutting points, which, 

 however, are bluntly bifid at their points. The marginals are in oblique, curv- 

 ing rows, gradually decreasing in size of the teeth as they pass off laterally. 

 They do not first increase and then decrease, as in Zonites and Glandina, or 

 not, at all events, to the same degree. In V. limpida, as stated below, the 

 seventh marginal appears, however, to be the largest. 



Vitrina has a world-wide distribution. In North America it is restricted 

 almost exclusively to the Northern Region, excepting on high elevations. 



Vitrina latissima, Lewis. 



Shell vitrinaform, very much depressed, thin, fragile, translucent, polished ; 

 suture deeply impressed ; whorls 2, very rapidly expanded, with delicate lines 

 of growth and quite conspicuous, separated, deeply impressed, 

 arcuate, transverse lines, and crossed by a few, microscopic, 

 impressed, revolving lines ; aperture nearly equal to half the 

 area of the base of the shell, very oblique, unsymmetrically 

 ovate ; peristome thin and acute, flexuose above and at the 

 columellar origin arising from the axis of the shell ; axis im- 

 perforate ; color of the shell amber brown. Transverse diam- 

 eter, 17.3 mill.; lesser diameter, 11.9 mill; height, 7.1 mill. 



Tennessee Bald Mountain, G,G00 feet. A species of the 

 Cumberland Subregion. 

 Vitrina latissima, Lewis, Proc. Acad. Nat. Sc. of Phila. 1875, 336, PI. XXIII. 



Fig- 7. 

 Fig. 51 is drawn from the original specimen. I regret not having had an 

 opportunity of seeing the animal, to verify its generic position. 



Vitrina limpida, Gould. 

 Vol. III. PI. LXVII. a, Fig. 1. 



Shell globose-discoid, thin, fragile, transparent, shining ; whorls 2\ to 3, 

 scarcely convex, with very minute lines of increase, the last whorl large and 

 much expanded ; suture not much impressed, sometimes with an impressed line 

 revolving near it; aperture large, subovate, somewhat diminished by the in- 

 trusion of the penultimate whorl ; peristome thin and acute, the columellar 

 margin a little reflected ; axis imperforate. Greatest transverse diameter nearly 

 6 mill. 



Vitrina pellucida, DeKay, N. Y. Moll., 25, PI. III. Fig. 42 (1843), not of 

 Muller. — Adams, Sh. of Vt., 162. — Binney, T. M., II. 58, PI. LXVII. 

 a, Fig. 1. 



V. latissima. 



