176 
HELICID^. 
those shells by the front of the last whorl being 
convex 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. 
Draparnaud erroneously describes this shell as 
having a clausium. (See Ferussac^ Essai^ hi.) 
82 , 1. Bale A perversa. Fragile Moss Shell. — 
Shell rather linear-oval, transparent yellowish ; 
whorls six or seven ; mouth subquadrate, (t. 6. 
f. 70.) 
Turbo perversus. Linn. S. N, 1240.; Mont. p. 335. t. 11. 
f. 12., Supp. 131. — Pupa fragilis. Drop. Hist. p. 68. t. 4. 
f. 4. — Clausllia fragilis. Feriiss. Bssai, 51.; Studer ; Jef- 
freys., Linn. Trans, xvi. 351. — Balaea fragilis. Leach., Moll. 
p. 116.; Alder., Cat. 8. 427. ; Mag. Zool. and Hot. ii. 111.; 
Forbes and Hanley., B. M. iv. 114. t. 128. f. 8, 9.- — Balea 
fragilis. Gray., Zool. Journ. i. p. 61.; Rossm. Icon. x. f. 638. 
— Balea perversa. Leach., Syn. Moll. 83.; Flem. B. A. 271. 
— Clausilia uniplicata. Calcara., 82. — 'Odostomia perversa. 
Flem. Ed. Ency, vii. 76. — Pupa perversa, Moq. Tand 
Moll. F. ii. 349. t. 25. f. 6. 14. — Bulimus perversus. Poiret., 
Prod. 57. ■— Clausilia parvula. Gart. Conch. Wett. 22. — 
—Clausilia perversa. Charpent. — Fusulus fragilis. Fitz. 
Syst. 108. — Stomodonta fragilis. Mermett., Moll. Pyr. 43. 
On the trunks of trees, under the bark, and em- 
bedded in the lichen ; also in the fissures of rocks. 
Animal brownish yellow ; neck black ; foot grey, 
granular, spotted, narrow, and elongate ; tentacles — 
upper thick, short, clavate, — lower scarcely visible, 
very small, tubercular ; muzzle very blunt and large. 
