394 HELICIDiE. 



straight transrersc scries ; uncini long, curved, thorn-shaped, biden- 

 tate, in a curved transverse series, and diminishing in size as they 

 pass off laterally. 



Vitrina limpida. 



Shell globose-discoid, thin, fragile, transparent, shining ; whorls two and a half 

 to three ; aperture large, sub-ovate ; lip thin, acute ; imperforate. 



Vitrina pellncida, Adams, Shells of Vermont, 162 (1842). — De Kay, N. Y. Moll. 2.5, pi. 



3, fig 42 (1843), not of Muller. — Binxey, Terr. Moll. ii. 5.5, pi 67 «, fig. 1 (1851). 

 Vitrina Americana, Pfeiffek (Dec. 1852), Proc. Zool. Soc. 156; in Che.mnitz, 2d ed. 



9, pi. 1, figs. 22-25 (1854). 

 Vitrina limpida, Gould, in Agassiz, Lake Superior, 243 (1850); Terr. Moll. 1. c. — ■ 



Pfeiffer, Malac. Blatt. ii. 10(1856); Mon. Hel. Viv. iv. 798. — W. G. Binney, 



Terr. Moll. iv. 33. — Reeve, Con. Icon. 62. — Morse, Journ. Portl. Soc. i. 11, pi. 



5, fig. 17 (1864) ; in Amer. Nat. i. 314, fig. 20 (1867).— Tryox, Am. Juurn. Conch. 



ii. 243, ]A. 3, fig. 1 (1866). 



Shell globose-discoid, thin, fragile, transparent, shining ; whorls 

 two and a half to three, scarcely convex, with very minute lines of 

 increase, the last whorl large and much expanded ; 

 '"■ ■ suture not much impressed, sometimes with an im- 



pressed line revolving near it ; aperture large, sub- 

 ovate, somewhat diminished by the intrusion of the 

 penultimate whorl ; peristome thin and acute, the 

 columella margin a little reflected ; axis imperforate. Greatest 

 transverse diameter nearly six millimetres. 



Animal whitish, grayish, or blackish, large compared with the 

 shell. Head, eye-peduncles, and eyes black ; tentacles very short. 

 The prolongation of the mantle extends from under the shell, over 

 the back and neck to the base of the eye-peduncles, but is unat- 

 tached and free ; from the right side of the mantle posteriorly, there 

 arises a tongue-shaped process, which is reflected back upon the 

 shell, and reaches to the spire. Respiratory foramen in the poste- 

 rior part of the mantle. 



Found in Maine, Vermont, New Brunswick, and to the northwest 

 of Lake Superior. An accidentally introduced colony has lately 

 been found by Dr. Lewis at Mohawk, New York. 



Oeiiiis HYALINA, (Fe'russac) Gray. 1840. 



Animal as in Helix. 



Shell generally umljilicated, thin, shining, greenish or reddisli horn 

 color ; whorls five to seven, regularly increasing, the last not de- 



