GASTEROPODA PULMONEA, 



349 



We ought to arrange near tliem some Helices which, without having a double-edged cloak, are equally incapable 

 of retreating within their shell. Helix rufa and brevipes, Ferns., are examples. 



When the depth of the aperture is greater than its w idth, as is always the case in shells with an oblong or elon- 

 gated spire, they are the terrestrial Bulhni of Brug., which it appears necessary to subdivide as follows ; — The 

 Bulbnus, Lam., have an oval rim, thickened in the adult, but without denticulations. In tropical countries, there 

 are some large and beautiful species ; some remarkable for the size of their eggs [equal to that of a Pigeon], and 

 with an equally solid shell ; and others for their reversed shells. In our own country there are several of small or 

 moderate size, and one of them (Helix decollata, Gm.) has the singular habit of breaking oft" in succession the 

 whorls from its spire. This example has been quoted as a proof that the muscles of the animal can be voluntarily 

 detached from the shell ; for a time does come when this Buliraus preserves no more than a single whorl of all 

 those it possessed at the beginning of the decollation. 



The Pupa, ham., have an obtusely-pointed shell, whose last whorl is narrower than the penultimate, whence 

 it has an elliptical, or sometimes a cylindrical form. The mouth is surrounded by a thickened rim, and en- 

 croached upon, on the side of the spire, by the penultimate whorl. The species are very small, living in moist 

 stations, amongst mosses, &c. There is sometimes no toothlet in the aperture, but oftener there is one or more 

 either on the projecting part of the penultimate whorl, or within the outer margin. [The genera Vertigo, Miill., 

 and Altea, Jeffreys, appear to have been separated from Pupa on too slight grounds ; for the inferior tentacula are 

 not absent, as is alleged, but only reduced to a minimum. The Partula, Per., deserves probably to be kept dis- 

 tinct ; for the species are ovo-viviparous, while all the others are oviparous.] 



The Choiidriis, Cuv., has, as in these latter Pupae, the mouth of the shell encroached upon by the penultimate 

 whorl, and guarded with plates or toothlets ; but the figure of the shell is more ovate, and more like that of the 

 common Bulimi. Some have the teeth on the rim of the aperture, and others have plaits situated deeper within 

 it. [This genus appears to be synonymous with the Azeca of Leach.] 



Here terminates the section of terrestrial Helices whose shell has a thickened oral rim \pT peritreme] in the adult. 



The Succinea, Drap., has an ovate shell, with an aperture longer than its width, as in Bulimus, but larger in 

 proportion ; the outer lip sharp, and the side of the columella almost concave. The Snail is too large to be con- 

 tained in it, and we may almost regard it as a Testacella with a big shell. The inferior tentacula are very small. 

 It lives upon the herbs and the shrubs of the brinks of rivulets, whence it has been considered as an amphibious 

 genus. 



We ought to separate from the genus Turbo of Linnaeus, and approximate near the terrestrial 

 Helices, the 



Clausilia, Drap., — 



Known by the slender, long, and pointed shell, with the last whorl narroAver than the penultimate in 

 the adult, compressed, and a little detached. Its mouth is entire and margined, and often toothed or 



furnished with plates. There is mostly found, 

 within the last whorl, a little lamina [commonly 

 termed the clausium'], slightly curved, a little 

 like the letter S, the use of which to the animal 

 is unknown to us.* The species are small, and 

 live in moss, at the foot of trees, &c. A great 

 number of them are reversed. 



The Achatin.\, Lam. — 

 Ought likewise to l)e separated from the Bulltp of 

 Linnaeus, and brought hither. The oval or ob- 

 long shell has the aperture of Bulimus, but is not 

 margined ; and has the extremity of the colu- 

 mella truncated, which is the first index of the 

 emarginations we find in so many of the shells 

 of the marine Gasteropodes. These Achatins 

 are large Snails which feed on trees and shrubs 

 in hot climates.f Of such as have, within the 

 last whorl, a callus or jiarticular thickening, 

 Montfort makes his genus Liguits. The body- 

 wliorl is proportionably narrow ; and when the 

 Fig. iGO,-A. zebra Fig. iGi.-A. virfinca. end of tlic Columella is curved towards the in- 



side of tlie aperture, and the body-whorl is broader, the species constitute iMontfort's Polyphemes. 



♦ 'I'lip usi- is to close the ajicrture of tlie shell when the Snail has shells : some are West Indian, and a very few Ruropcan. Among the 



retired. See a good description of its mechanism by Mr. J. K. Gray, Utter, wc can only lay claim to one as decidedly a native of tlii:* 



in '/.(ml. Jonrn. vol. i. p. 212. — Kd country, the A. aricula of Lamarck."— En. 



i " The greater number of Achatina?," says Sowcrby, " are African 



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