ACHATISA.- 



-MOLLUSCA. Lym.n.ea. 



355 



occuiTcd, where they have remained in a state of deep 

 slumber for the space of twenty months. Their eggs are 

 sometimes very large, and are covered externally with a 

 hard calcareous shell. Those of BuUmus hamastomus 

 are almost as large as a pigeon's, and nearly as hard. 

 It appears that the tropical, and more especially the 

 arboreal species, cement leaves of trees together, curl- 

 ing one upon another, so as to form an artificial nest 

 for the reception of these large eggs. 



Genus Achatina. — The Agate shells have a shell 

 a good deal resembling the Bulimi ; but they are thinner, 

 and the culuraclla is twisted, and more or less abruptly 

 truncated in front. The shell is not unibilicated ; the 

 aperture is oval, elongate, and the peristome is thin, 

 acute, and not reflected, the margins united by a dif- 

 fused callus. The Aohatinie are numerous in species, 

 upwards of one hundred and twenty having been de- 

 scribed, and some of the African ones are the largest 

 terrestrial shells known. They attain the length of 

 tiglit inches, and their eggs, which are calcareous like 

 tliose of the Bulimi, are sometimes more than an inch 

 in length. They are chiefly found about trees near 

 water, and the great majority are natives of Africa. The 

 genus is represented on Plate 7, fig. 8 (-4. Virginia). 



Genus Pupa. — The Pupae have a solid, cylindrical, 

 or oblong-ovate shell, with many whirls, a conical ape.x, 

 and a rounded, often toothed aperture. The base is 

 rimate or, rarely, umbilicated, and the surface of the 

 shell is generally very closely ribbed with straight ridges. 

 The species are numerous, amounting to upwards of 

 one hundred and sixty, and are found in all the four 

 quarters of the globe. The genus is represented on 

 Plate 7, tig. 9 {Pupa mumia). 



Genus Clausilia. — The Clausilias have a fusiform 

 shell, almost always sinistral, or turned to the left. 

 The aperture is elliptical or pyriform, provided with 

 two plaits or lamellie which contract the margin, and 

 is closed at the bottom, or in the neck, by a movable 

 shelly plate, called a clausium. This peculiar organ is 

 attached to the pillar of the shell by a slender pedicel, 

 and is placed in such a position as to shut the throat 

 of the shell, when the animal is inclosed, while at the 

 same time the animal can push it on one side, when it 

 wishes to come forth in search of food. The species 

 are very numerous, upwards of two hundred having 

 been described, and are distributed over the four quar- 

 ters of the globe, though most numerous in the tem- 

 ])erale countries of Europe. This genus is represented 

 on Plate 7, by fig. 7 [Clausilia carulea). 



Genus Cylindrella. — The Cylinder shells differ 

 from the Clausilias, chiefly in wanting the plaits or 

 lamella; in the aperture. The shells are generally long 

 and cj'lindrical, many-whirled, the apex in the adult 

 generally broken ofl'; or truncated while the mouth is 

 round, and the peristome expanded and continuous. 



L1.MNOPHILA, Fresh-water Snatls. — The animals 

 belonging to the second group have subcylindrical or 

 flattened tentacles, which are simply contractile, and 

 have the eyes placed sessile on their base. 



Family— AURICULID.<E. 

 The Auriculas have a ringed conical muzzle, and a 

 thin mantle with a thickened edge. The shell is spira), 



covered with a horny epidermis, and has the mouth, 

 which is elongate, furnished with strong plaits on the 

 columella. The outer lip is also in many cases toothed, 

 or transversely ribbed. The animals are peculiar in 

 having the power of absorbing progressively the septa, 

 or divisions, which separate the cavities of the whirls 

 from one another. With few exceptions the species, 

 wliich are numerous (upwards of two hundred having 

 been described by PfeiCfer in the Catalogue of Auri- 

 culidcE in the collection of the British JIuseum), are 

 natives of tropical countries, and live in brackish-water 

 marshes, estuaries, and mouths of rivers, clinging to the 

 stems and roots of mangroves ; among loose stones above 

 high water mark, but within the influence of the tide ; 

 or in damp woods near the sea. 



Family— LYMN^ID^. 



The Pond Snails have a short dilated muzzle, fl.it- 

 tened tentacles, and a flattened, lanceolate, or oval foot. 

 The shell is thin, horn-coloured, rather varied in form, 

 but usually with an oblique fold on the columella, and 

 a simple, acute outer lip. The species are numerous, 

 and are all fresh-water animals, living in the water, but 

 coming to the surface to breathe. They are found in 

 all parts of the world, and inhabit ponds and running 

 streams. They are chiefly found in temperate coun- 

 tries, and are for the most part phytophagous or veget- 

 able feeders. They deposit their ova on the stems and 

 leaves of the weeds which grow around them, enveloped 

 in an oblong gelatinous nidus. The form of the shell, 

 as we have said, is very varied. 



Genus Lymn.ea. — The LymnoQa.- have a spiral, dex- 

 tral shell, more or less elongated, thin, horn-coloured, 

 and translucent. The last whirl is large, ventricose, the 

 aperture large, rounded in front, the columella obliquely 

 twisted, and the outer lip simple and acute. The species 

 are upwards of fifty in number, and are found in most 

 temperate countries of the globe. Their food consists of 

 both vegetable and animal matter, one species feeding 

 on the green fresh-water algae, while others prefer animal 

 food. This peculiarity in their diet has caused them 

 to be denominated " the scavengers of the waters;" and 

 Mr. Jeffreys informs us, that in the absence of other 

 nourishment, "they will even devour each other, piercing 

 the shell near its apex, and eating away the upper folds 

 of its inhabitant." Although generally to be seen 

 creeping on the muddy bottoms of ponds and streams, 

 and on the stones, or on the leaves and stems of sub- 

 merged plants, they always come to the surface to 

 respire free air, and can, when there, to use Dr. John- 

 ston's words, " make the water a liquid pavement," along 

 which they creep by an undulatory motion of the foot, 

 but with the body and shell in a reversed position. 

 " When thus suspended, they will sometimes relax their 

 hold and drop at once to the bottom, from which in 

 general they emerge by crawling up some solid body ; 

 but occasionally I have seen them rise up direct througli 

 the water." — {Jolaislon.) When the ponds are dried 

 up, the Pond Snails bury themselves in the mud, 

 strengthen the outer lip by an internal rib, and cover 

 the mouth by means of a membranaceous cpiphragm, 

 like the land snails. 



