340 



Div. 2. MOLLUSCA— GASTEROPODES. 



Class 3. 



Fig. 158.— Tlic Test»c*lU 



The Vaginulus, Peruss.* — 

 Has a close-fitted cloak without a shell, extended over the whole length of the hody ; four tentacula, 

 of which the inferior are somewhat forked ; the anus quite at the posterior extremity, between the end 

 of the cloak and that of the foot ; and the same orifice leads to the pulmonary cavity situated along 

 the right flank. The orifice of the male organ of generation is under the right inferior tentaeidum, and 

 that of the female organ under the middle of the right side. These organs, as well as those of digestion, 

 are very similar to those of the Snail. The genus belongs to both Indies, and is much like our Slugs. 



The Testacell^, Lam. — 

 Have the respiratory aperture, and the anus, near the posterior extremity ; their cloak is very small, 

 and also placed there, and contains a small ear-shaped shell, which does not equal one-tenth of the 

 length of the body. In other respects, these animals resemble our Slugs. 



One species is found abundantly in our southern 

 departments (Testacella haliotoidea, Diapain.), 

 living under ground, and feeding principally 

 on earth-worms. M. de Ferussac has observed 

 that its cloak assumes an extraordinary develope- 

 ment when the animal tind.s itself in too dry a 

 situation, and thus produces for itself a sort of 

 shade and shelter. 



[There are some interesting illustrations of the 

 habits of the Testacellaj in Loudon's Magazine 

 of Natural History, vol. vii.] 



The Parmacella, Cuv. — 

 Has a membranous cloak, with loose margins, situated [upon a gibbosity] in the middle of the back, 

 and containing, in its posterior part, an oblong flat shell, which exhibits the mere vestige of a spine. 

 The respiratory aperture, and the anus, are under the right side of the middle of the cloak. 



The first known species was from Mesopotamia {Par. Olivieri,CviV.); but we have now one from Brazil, and 

 some others from India. 



In the terrestrial Pulmonea with a perfect and exterior shell, the margin of its aperture is in general 



thickened and reverted in the adult. 



Linnaeus referred to his genus 



Helix, — 



Every species in which the aperture of the shell (somewhat encroached upon by the projection of the 



penultimate whorl) assumes a crescent-like figure. 



When this lunated aperture is wider than it is deep, the shells belong to Helix, Brug. & Lam. In some, the 

 shell is globular. Everybody knows the edible Snail (Uel. pomatia, Linn.), common in gardens and vineyards, 

 and esteemed as a delicacy in some departments ; and the common Snail {Uel. Jiemoralis, Linn.), remarkable for 

 the vividness and variety of its colours, and very 

 liurtful to garden stuffs in wet seasons. There is 

 no one who has not heard of the curious experi- 

 ments, showing to what extent they can reproduce 

 amputated parts. 



Other species have a depres.sed shell, or one with 

 a flattened spire ; and we ought not to pass over 

 without notice such as have interiorly projecting 

 ribs, nor those in which the last whorl is abruptly 



turned up in the adult [so that the aperture appears ,,,g 153 _a„..,„,„, g.„bu,. 



In the same plane as the spire], and then assumes 

 an irregular plicated form,— hence denominated Anasioma\ by Lamarck. 



The Yitrina, Drap. (llelico-Limax, Feruss.), are Helices witli an extremely thin subspiral shell, without an urn- 

 bilicus, and with an ample aperture, whose margin is sharp and even. The body of the Snail is too large to be 

 drawn within the shell. The cloak has a double edge; and the superior fold, which is divided into several lobes, 

 may be made to overlap the shell so as to clean and polish it. The European species live in moist situations, and 

 are very small ; but there are some of large size in warm climates. 



• Synonymnus with the Onchidium of Buchaimii ; nnd the I'erimi- 

 C'Ui of ISIaiiiviUe is not difffrcnt.— En. 



t "The pi'culiarity which dislinniiisliej this Rcnus from nil the other 

 H-liciform Univalves is .10 extraordinary, that it appears to us to be 

 ilfscrvirg of particular notice, inasmucli as it evidences a consiiier- 

 ible alteration in the hiibil and economy of the animal which proiluces 

 tt. at the lime of its arrival at its last period of growth, when it forms 



the reflected outer lip, and the teeth in the aperture. Until then, the 

 animal must crawl about like other Snails, with the spire of its shell 

 uppermost ; but as soon as it arrives at maturity, and is about to form 

 its complete aperture, it takes a reverse position, and atterwards 

 constantly carries its spire downwards."— Sowkmdy. Two species 

 are known — £0 



