226 LECTURES ON MOLLUSCA. 



not be seen. Boysia is a Pupa, with the mouth turned up, as in 

 Anostoma. Gibbus is a group of irregular shells, intermediate between 

 Pupa and Bulimus. The shells of Clausilia are drawn out at each 

 end, and are always reversed. The animals have the great peculiarity 

 of having a kind of operculum (clausium) which moves on a leathery 

 hinge, and fits between the teeth of the mouth. They greatly abound 

 in the old world; but only three species have been found in the whole 

 of America. They are represented in the West Indies by the beautiful 

 group Cylindrdla, in which the mouth is round and the lip reflected. 

 The upper whirls, which would make the shell too long to be carried, 

 are generally thrown off; but the mouth in some species is produced to 

 so enormous a distance that the animal must carry its shell poised in 

 the air, like a pole held at one end. The polished Cylindrellas are 

 called Leia, answering to Zua among the Bulimi. The little reversed 

 shells of Balea are like a young Clausilia; and Megaspira is like a 

 very produced Pupa, with plaits on the pillar. 



The next group consists of snails, which, though they do not live in 

 the water, are never found far off. Their eye-tentacles are short and 

 stumpy, and the animal is fleshy, and not fully drawn into the shell. 

 This is scarcely calcareous, being rarely more than a spiral skin, 

 generally of an amber color. The Succineas are very common in 

 marshy places, and easily known by the very loosely spiral shell, with 

 long mouth and pointed spire. Amphibulima has the mouth expanded 

 and pinched at the top. Simpulopsis has more the shape of ordinaiy 

 snails. In Helisiga the spire is extremely small; and in Omalonyx it 

 is almost obsolete, the mantle of the animal being reflected over the 

 sides, as in Vitrina. 



Family Vitrinid^;. (Glass-snails.) 



The Vitrinas are intermediate between snails and slugs. ' They can 

 never entirely enter their shells ; and, when they crawl, the sides of 

 the mantle more or less overlap the edges. The shells, like those of 

 jSuccinea, are little more than spiral skins, and are generally snail- 

 shaped, and green. A passage to the true snails is provided in Pfeif- 

 feria. In Daudebardia, the tail is very short; the little shell lying 

 at the back of the animal, ajs in Testacellus. The shell of Peltella is 

 shaped like the Sea-ears, and is entirely hidden by the mantle. Cryp- 

 tella is the slug of the Canary Islands, which hides itself the greater 

 part of the year, and then makes sad havoc of the gardens in the rainy 

 season. It has an irregular shell, which in the very young state is 

 provided with an operculum ; but afterwards it is entirely covered by 

 the mantle-shield, on the back of the broad animal. The African tribe 

 Parmactlla, have a similar shell, similarly hidden. The foot is trun- 

 cated behind, thus passing into the next group. 



Some of the Vitrinas have the tongue-teeth hooked at the sides, and 

 are supposed to feast on animal substances. The Stenopus tribe how- 

 ever have a horny, saw-shaped jaw and teeth, after the model of the 

 true snails. They resemble the Vitrinai in having mantle-flaps partly 

 .covering the shell; but differ in having the foot truncated behind, 

 with a slime-gland at the end. The shells are horny and polished 



