MALACOZOA. GASTEROPODA. PULMOBRANCHIATA. 119 



decayed leaves of trees ; in June by Miss Macgillivray in a 

 stripe of the Don, near Seaton House; in July by myself in 

 the Loch of Skene, the Inverury Canal, and subsequently in 

 many other locaHties, it being generally distributed in the 

 lower tracts. 



Plauorbis contoi-tus. ?.Iuller, Verm. Terr, et Fhiv, ii. 162. — 

 Planorbis contortus. Linn. Syst. Nat. i. 1244. — Helix contorta. 

 Mont. Test. Brit. 4o7. PI. 25, f. 6. — Planorbis contortus. Drap. 

 Moll. Terr, et Fluv. 42. PL I. f. 39,40, 4 1 .—Planorbis contortus. 

 Lamk. Syst. vi. 2. 154. Ed. n. viii, 387. — Planorbis contortus. Fie m. 

 Brit. Auim. 277. — Planorbis contortus. Gray's Turtou, 270. 



3. Planorbis dlbu^. Bristly Coil-Shell, 



Shell widely concave above and beneath, with three and a- 

 half or fovu- rapidly increasing volutions, which are convex on 

 both sides, longitudinally finely sulcato-striate, minutely striate 

 transversely, delicately hispid with tapering shreds of the epi- 

 dermis ; the last turn disproportionately enlarged, considerably 

 depressed, with the outer margin convex ; the mouth a little 

 oblique, semiovate or nearly elliptical, dilated, with the peri- 

 stome somewhat thickened and slightly spreading ; the colour 

 pale horny or yellowish-grey. Diameter two-twelfths and a- 

 half, height nearly a fourth of the breadth. 



The animal in walking in the water bears the shell inclined 

 at an angle varying from 70° to 80°, the right margin, as usual, 

 touching the ground, or other surface. Out of the water, it 

 drags the shell, laid flat, by sudden jerks. The foot is ovato- 

 triangular, pale grey beneath, brown above, in length about a 

 third of the diameter of the shell. The neck is short, dusky ; 

 the head oblong in front, dusky, with a large em.aryinate veil ; 

 the tentacula subulato-setaceous, pale grey or white, with a 

 medial brown line, dilated and transparent at the base, on the 

 inner side of which is the small black eye. The head, and 

 especially the veil, can be expanded to a great breadth. This 

 species is found with us on various species of Potamogeton, as 

 well as other plants, particularly Veronica Beccabunga and 

 Poa fluitans, on which it feeds. 



First found by me in the Aberdeen Canal, on the 22d of 

 August, 1812. 



It occurs abundantly there, chiefly on the different species 

 of Potamogeton, on the foliage of which it feeds, with great 

 voracity, as I ascertained by keeping it alive for many days. 

 Its actions are similar to those of the species already described. 



