helicid^:. 207 



13. Balnea. (Moss Shell.) 



The animal is like Bulimus, but the shell is reversed, 

 thin, with an elongated taper spire, the last volu- 

 tion larger than the next; aperture roundish-oval, 

 entire at the base, oblique, with a single tooth on 

 the pillar, which is wanting in the young shells, 

 and the pillar is destitute of any valve-like plait or 

 clausium. 



This shell is often mistaken for a young unformed 

 specimen of Clausilia, but it may be known from 

 those shells by the front of the last whorl being con- 

 vex and simple, and not flattened and furnished 

 with a keeled ridge near the outer edge, as is the 

 case with the young of all the species of that genus. 



From Bulimus and Pupa this genus is distinguished 

 by the aperture being left-handed; from Clausilia, in 

 having the ultimate volution proportionately larger 

 than the next; and from Vertigo, in the regularity of 

 its mouth. 



77. 1. Balnea perversa. Fragile Moss Shell, (t. 6. 

 f. 70.) Shell rather linear-oval, transparent yel- 

 lowish; whorls six or seven; mouth subquad- 

 rate. 



Balasa fragilis. Leach, Moll. p. 116.; Alder, Cat. 

 8. 427.; Mag. Zool. $ Bot. ii. 111. 



Balea fragilis. Gray, Zool. Journ. i. p. 61. 



Pupa fragilis. Drap. p. 68. t. 4. f. 4. 



Turbo perversus. Mont. p. 335. t. 11. f. 12. 



Balea perversa. Flem. B. A. 



Odostomia perversa. Flem. Ed. Ency. 



Clausilia fragilis. Studer ; Jeffreys, Linn. Trans. 

 xvi. 351. 



