Order 1. 



GASTEROPODA PULMONEA. 



341 



We ouaflit 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, Ferus., are examples. 



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

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

 BuUmiis, 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 off in succes^sion 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 Bulimus preserves no more than a single whorl of all 

 those it possessed at the beginning of the decollation. 



The P«^«, Lam., 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 Ahca, 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, Fer., deserves probably to be kept dis- 

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



The Chondrus, Cuv., has, as in these latter Pupas, 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 [or peritreme] in the adult. 



The Snccinea, 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. 



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



Ilehces, the 



Clausilia, Drap., — 



Known hy the slender, long, and pointed shell, with the last whorl narrower 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. 



Fig. 160. — \, zebra 



Fig. 161. — A. virginea. 



The Achatina, Lam. — 

 Ought likewise to be separated from the EulUs of 

 Linnaeus, and brought hither. The oval or oli- 

 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 Achatina; 

 are large Snails which feed on trees and shrubs 

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

 last whorl, a callus or particular thickening 

 Montfort makes his genus Liguus. The body- 

 whorl is proportionably narrow ; and when the 

 end of the columella is curved towards the in- 



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



• The use is to close the aperture of the shell when the Snail has 

 retired. See a good description of its mechanism by Mr. J. E. Gray, 

 in Zool. Jottrn. vol. i. p. 212. — Ed 



* " The greater number of Achatina,'* says Sowerby, " are African 



shells : some are West Indian, and a very few European. Among the 

 latter, we can only lay claim to one as decidedly a jiative of thitt 

 country, the ^1. aricula of Lamarck."- En. 



