Gasteropoda.- 



-MOLLUSCA.- 



-Paludinidjs. 



339 



slight canal in front. The opercnlum is horny, spiral. 

 The species are niimeroun, about seventy having been 

 enumerated, and are Ibnnd distributed throughout all 

 parts of the world. They are most abundant, however, 

 in the north temperate zone, and live among sea-weed 

 in shallow water. 



Family— MELANIID^. 



This is a numerous family, containing within it 

 upwards of one hundred and si.^ty species. The shell 

 is spiral, turreted, and covered with a dark olive 

 epidermis. The aperture is ovate or circular, some- 

 times entire in front and at others channeled ; and the 

 operculum is ovate, horny, and spiral. The animals 

 of this family are fluviatile, being inhabitants of fresh- 

 water lakes and rivers throughout the warmer regions 

 of the globe; and the apex of the spire of the shell is 

 often eroded by the action of the water in which they 

 live. In the southern states of North America they 

 are numerous and form peculiar groups. Some of 

 tlie species are viviparous. The animal of one species, 

 Melania amarula, is very bitter, and in the Isle of 

 Bourbon and some of the adjacent islands it passes 

 for an excellent remedy for the dropsy. The variety 

 of form which characterizes many of the shells has 

 necessitated their being grouped in difl'erent genera, 

 and a good many have accordingly been formed. The 

 principal character depended upon for dividing them 

 is the form of the aperture. The family is represented 

 in Plate 1, figs. 1 and 2, by Melania [hibex] Byronensis. 



Family- CERITHIID.E. 



The Ceritbia have the sliell ovate, spiral, many- 

 whirled, and covered with a thin epidermis. The 

 aperture is ovate or subquadrate, and more or less 

 channeled in front. The outer lip is often expanded, 

 especially in adult specimens. The operculum is 

 horny and spiral. The species are numerous, upwards 

 of one hundred having been described, and they pre- 

 sent various modifications of form and habits of life. 

 Two forms are represented in Plate 1, figs. 1 and 2, 

 by Cerithium leave and Tympanotomus muricatus ; and 

 the operculum is represented by that of Telescopium 

 ftiscwn in fig. 3. The operculum here offers a good 

 character for assisting in separating them into groups. 

 Some of the species are marine in their mode of life, 

 while others dwell in the mouths of rivers or in salt 

 marshes. Some of the marine species emit a green 

 fluid when molested, which becomes purple in drying. 

 "Two specimens of Cerithium armalum were brought 

 alive to London from the Mauritius," sa3's Dr. Johnston, 

 " kept, during their long voyage, in a dry state, 

 affording a remarkable illustration of tenacity of life. 

 The animal was apparently healthy, and beautif\illy 

 coloured. It emitted a considerable quantity of bright 

 green fluid, which stained paper of a grass-green 

 colour. It also coloured two or three ounces of pure 

 water. This green solution, after standing for twelve 

 hours in a stoppered bottle, became purplish at the 

 upper part ; but the paper retained its green colour 

 tliough exposed to the atmosphere. A tincture made 



by immersing the animal of Ceril/iiiim Idescopiwa in 

 spirits, became of a dark verdigris colour, which it 

 retained for some weeks." These shells are found in 

 all parts of the world, the typical species, however, 

 being tropical. 



The ihiviatile or salt-marsh species, forming the 

 genus Telescopium, are few, and are found inhabiting 

 the salt marshes and swampy tracks near the mouths 

 of rivers in the East Indies and their islands. There 

 thoy may be seen, with their pointed spires sticking 

 out of the mud, in incredible numbers. We have 

 seen them in great abundance on the muddy shores of 

 Saugor island at the mouth of the river llooghly in 

 the Bay of Bengal ; and we are told that their numbers 

 are so great that they are collected for the purpose of 

 being burnt into lime. Great heaps are formed and 

 exposed to the sun to kill the animals. In the island 

 of Borneo the animals are eaten \ty the i ativcs. 



Family— TURRITELLIDiEi. 



The family of TURRET or SCREW SHELLS {Turri- 

 lellidiE) have the operculum horny, circular, and many- 

 whirled, the whirls fringed on the edge. The shells 

 are spiral, many-whirled, imperforate, and the aper- 

 ture is rounded and simple in front. This is strictly 

 a marine family ; the species, which are tolerably 

 numerous — upwards of fifty having been described — 

 ranging from low-water mark to the dejith of one hun- 

 dred fathoms. Their geographical distribution is world- 

 wide, one species living in our own seas. The term 

 " Screw-shells," by which they are familiarly known, 

 is derived from their peculiar spiral form. Tbcy live 

 buried and fixed in tenacious mud, mixed with shelly 

 debris, and can only protrude the head and tentacles 

 from the mass. They walk very slowly, owing to the 

 shortness of the foot. 



Genos Tuuritella. — This genus gives its name to 

 the fiimily, and contains a considerable number of 

 species, the shells of which are turreted, and have a 

 subquadrate-sbaped aperture, simple in front. They 

 are chiefly natives of tropical countries. 



Passing over the family BARLiEIDa!, the species of 

 which are few, small, and obscure, we come next to tlie 

 KivER Snails :— 



Family PALUDINID^ (Vioiparulce). 



In this family tlie shell is spiral, turbinate, covered 

 with an olive-coloured epidermis. The aperture is 

 ovate and simple in front. The species of River 

 Snails, amounting to upwards of sixty, are fluviatile, 

 inhabiting lakes and streams over the greater part of 

 the world. They have a good deal the external 

 appearance of the Apple Snails {Ampullariida:). — See 

 page 201. 



Genus Paludina {yivipants).—lh\s genus has 

 a thin, horny, annular operculum, with the nucleus 

 near the middle of the inner side— Plate 2, lig. 3. 

 The shell is ovate, thin, and covered with a thin 

 epidermis beset with hairy bands. The species inhabit 

 the rivers and lakes throughout the Northern hemi- 

 sphere. The animals are sluggish, feeding upon living 



