MALACOZOA. GASTEROPODA. PULMOBRANCHIATA. 105 



for Helices, with me, at the foot of the wall behind Old Machar 

 Cathedral ; afterwards gathered there by Miss Macgillivray 

 and myself. On the 18th of June, found by me among the 

 ruins of Dunottar Castle. 



Tnrbo perversus. Linn. Syst. Nat. i. 1240. Turbo perversus. 

 Mont. Test. Brit. 335. PI. 11. f. 12. Pupa fragilis. Drap. Moll. 

 68. PL 4. f. 4. Pupa fragilis. Lamk. Syst. vi. 2. 110; Ed. n. 

 viii. 178. Baleea perversa. Flem. Brit Anim. 271. Bakea per- 

 versa. Gray's Turtou. 207. 



SECTION II. AQUATICA. 



FAMILY III. LIMN^INA. 



Animal with the body ovate or elongated, spirally bent 

 or coiled, or conical, covered by the mantle, the thin 

 edge of which forms a circular collar around the neck ; 

 the head surmounted by a large expansion or veil ; two 

 generally depressed, contractile tentacula, having the eyes 

 situated near their base ; orifice of the pulmonary cavity 

 on the collar, near the anal aperture; genital organs 

 separated ; foot ovate or elongated, depressed. 



Shell delicate, fragile, spiral, involute, rarely conical, 

 of a uniform colour, with a firm, olivaceous, brownish, 

 or yellowish-grey epidermis ; the outer margin of its aper- 

 ture thin. 



The species live in brooks, rivers, ditches, pools, and 

 lakes, generally immersed in the water, and crawling on 

 the mud, on stones, or plants, but coming occasionally 

 to the surface to respire. They are capable of advancing 

 along the surface of the water with the disk of the foot 

 applied to it, "and the body reversed. Their food consists 

 of vegetable substances. 



GENUS 1. LIMN^EUS. MUD-SHELL. 



Animal oval, spiral; head with two flattened sub trian- 

 gular, obtuse tentacula, bearing the eyes at their base 

 internally ; mouth with an upper piece for mastication, 

 and surmounted by a short veil ; foot oval, anteriorly 

 two-lobed, narrowed behind; pulmonary orifice on the 



