120 MALACOZOA. GASTEROPODA. PULMOBRANCHIATA, 



As the shell is not really white, I think Mailer's name albus 

 ought to be rejected, and that of Draparnaud employed. 



Planorbis albus. Mull. Verm. Terr, et Fluv. ii. 164. — Planorbis 

 hispidus. Drap. Moll. Terr, et Fluv. ii. 43. PI. 1. f. 45, 46, 47.— 

 Planorbis hispidus. Lamk. Syst. vi. 2. 154. Ed. 2. viii. 387. — 

 Helix alba. Mont. Test. Brit. 459. — Planorbis albus. Flem. Brit. 

 Auim. 278. 



The shell when emptied is generally very pale yellowish or 

 greenish-grey, sometimes greyish-white ; when containing the 

 animal, dusky. 



4. Planorbis imbricdlus. Crested Coil-Shell. 



Shell flat, slightly concave in the middle, above, widely and 

 very deeply concave beneath, with three rapidly increasing, 

 depressed, obliquely sulcato-striate volutions, which are convex 

 above, sloping deeply to the suture, more convex beneath ; the 

 last turns disproportionately enlarged, depressed, sloping to an 

 obtuse medial angle, and much widened toward the mouth, 

 which is somewhat oblique, subelliptical, with the peristome 

 complete, a little thickened, and spreading or slightly reflexed ; 

 the colour pale yellowish-grey. Diameter two-twelfths of an 

 inch. 



In form and colour this shell resembles Planorbis albus; 

 from which however it is distinguished by the greater con- 

 cavity of its lower surface, by its having the turns more flat- 

 tened, the periphery with a kind of blunt keel, the mouth wider, 

 the peristome thicker, the turns destitute of spiral striae, and 

 strongly marked with transverse grooves, almost in the man- 

 ner of Zonites rotundatus. It appears to be Planorbis imbri- 

 catus of Draparnaud, with whose description and figure it 

 agrees in every particular, with the exception of the lamellar 

 epidermis, which may have been abraded, the specimen being 

 a dead one, and the "lames," according to him, being "tres- 

 caduques." 



Planorbis imbricatus. Drap. Moll. Terr, et Fluv. 44. PI. i. 

 f. 49, 50, 51.— Muller, Verm. ii. 165.— Gray's Turt. 261.— Lamk. 

 Syst. vi. 2. 155. 



Genus 4. Ancylus. Lid-Shell. 



Animal conoidal, with an elliptical outline beneath ; 

 head with two depressed, elongated, triangular, obtuse, 

 contractile tentacula, mouth with a flattened, carinate, 



