120 MALACOZOA. GASTEROPODA. PULMOBRANCHIAT^I. 



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

 ought to be rejected, and that of Draparnaud employed. 



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

 liispidus. Drap. Moll. Terr, et Fluv. ii. 4:3. PL 1. f. 45, 46, 47. 

 Planorbis liispidus. Lamk. Syst. vi. 2. 154. Ed. 2. viii. 387. 

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

 Anim. 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, 



