GASTEROPODA PULMONEA. 335 



slender and pointed, the last whorl, in the adult, narrowed, com- 

 pressed, slightly detached, and terminated by a complete aperture 

 with a tumid margin, frequently dentated or furnished with laminae. 

 In the contraction of the last whorl we usually find a little plate 

 bent into an S, the use of which to the living animal is unknown. 



The species are very small, living in mosses at the foot of 

 trees, &c. A great many of them are reversed(l). 



Ac HAT IN A, Lam. 



Necessarily separated from the Bullae of Linnaeus and placed here. 

 The aperture of the oval or oblong shell is higher than it is broad, 

 as in the Bulimi, but wants the tumid margin^ the extremity of the 

 columella also is truncated, the first indication of the emarginations 

 which we shall find in so many marine Gasteropoda. These Acha- 

 tinae are large Helices, which devour trees and shrubs in hot coun- 

 tries(2). 



Montfort distinguishes those, in the last whorl of which we find a 

 callus or peculiar thickening, — Liguus, Montf.(3)j this whorl is 

 proportionably lower in them than in the others: 



And those in which the extremity of the columella is curved to- 

 wards the inside of the aperture — Polyphemus, Montf.(4)j the last 

 whorl is higher. The 



PULMONEA AUUATICA 



Have but two tentacula, as already stated ; they are continu- 

 ally compelled to rise to the surface for the purpose of breath- 

 ing, so that they cannot inhabit very deep water ; they are 

 usually found in fresh water or salt ponds, or at least in the 

 vicinity of the sea coast and of the mouths of rivers. Some 

 of them have no shell, such as 



(1) Turbo perversus, L., List., 41, 39; — T. bidens, Gm., Drap., IV, 5, 7; — T. jyap- 

 illaris, Gm., Drap., lb., 13; and the other Clausilia: of Drap., figured on the same 

 plate; — Bulimus retusus, Oliv., Voy., XVII, 2; — Bui. injiatus, lb., 3; — Bui. teres, 

 lb., 6; — Bui. torticollis, lb., 4, a, b; — Turbo tridens, L., Chemn., IX, xli, 957; — 

 Clausilia collaris, F^russ., List., 20, 16. 



(2) Bulla zebra, L. Chemn., IX, ciii, 875, 876; cxviii, lOU— 1016;— Bulla 

 achatina, lb., 1012,1013; — Bulla purpurea, lb ., 1018; — Bulla dominicensis. Id., 

 CXVII, 1011; — Bulla stercus pulicum, CXX, 1026, 1027; — Bulla Jlammea, Id., 

 CXIX, 1021 — 1025; — Helix teticra, Gm., lb., 1028, 1030; — Bulimus bicarinatus, 

 Brug.jList., 37; — Melanie buccino'ide, Oliv., Voy., XVII, 8. 



(3) Bulla virginea, L., Chemn., IX, cxvii, 1000, 1003; X*, clxxiii, 1682, 3. 



(4) Bulimus glans,Bmg., Cliemn., IX, cxvii, 1009, 1010. 



