Gasteropoda.- 



-MOLLUSCA.- 



-LlTTOELNID.E. 



337 



curopccd) is a plain white sliell, but its snail is a verj' 

 elegant creature. The proboscis is dark vermilion ; 

 the tentacula yellowish-red, spotted with yellow ; the 

 upper part of the foot streaked longitudinally with 

 yellow and brown ; and the mantle greenish-brown, 

 edged with brownish-red ; but, notwithstanding, the 

 shell is a uniform dull white." — {Johnston.) 



Family— APORRHAID^. 



The family of Spout-shells (AjJOrrhaida:) have the 

 shells spiral when adult, and the canal is bent to the 

 right. The outer lip is expanded or revohite, some- 

 times lobed or digitated. The operculum is annular, 

 ovate, or pointed, with a small apical nucleus. 



Genus Aporrhais. — This genus, which gives its 

 name to the family, has the shell fusiform, the spire 

 elongated, with many tuberculated whirls, a narrow 

 aperture, a distinct canal, and the outer lip dilated 

 and lobed, or digitated. The operculum is ovate 

 pointed, and lamellar. There are only three species 

 known, two of which are natives of Great Britain and 

 the Mediterranean, and one of Labrador. 



THE APOERHAIS PES-PEUCANI, or Pelican's 

 Foot, is very common in Great Britain. The animal 

 creeps slowly, and is shy in its disposition. The shells 

 are subject to great variety with respect to the outer 

 lip. In the young shell there is not the least expansion 

 of the lip, but it increases by age. It is generally of 

 a dull white colour; but the animal has its rostrum 

 pink, dotted over with milk-white spots; the tentacles 

 are also of a pink colour, and the eyes black. 



Genus Strutiiiolaria. — The genus Struthiolaria, 

 or Ostrich's-foot shell, is more numerous in species 

 than Aporrhais, but they are exclusively confined to 

 Kew Zealand and Australia. The shell is ovate, with 

 a conic, acuminated spire. The aperture is ovate, with 

 a short indistinct canal in front, and the lips and 

 columella are thickened and polished. The operculum 

 is ovate, acute at the apex, with a broad notch on the 

 inner side near the tip. 



Genus Trichotropis.— This genus is composed of 

 top-shaped spiral shells, with keeled whirls, wdiich are 

 edged with a horny fringe, and covered all over with 

 an epidermis of the same substance. The species, 

 which are few in number, are chiefly from the northern 

 seas, where they inhabit deep water. 



In the preceding families of the Rostrlfera, the 

 mantle of the animal, when full-grown, is expanded, 

 and more or less reflexed over the shell. In those 

 which follow, the mantle is inclosed within the shell. 

 Some of them are inhabitants of the dry land, and 

 their breathing organs are adapted for respiring free 

 air. They are vascular, branched, and are placed on 

 the inner surface of the mantle, which is free from the 

 nape, and leaves the pulmonary cavity open. The 

 animals have distinct sexes, are oviparous, and possess 

 a well-formed spiral or annulated operculum. 



Family— CYCLOSTOMIDJS {Cyclophoridm). 



The animals belonging to this family have an elon- 

 gated foot and a spiral operculum. This operculum pre- 

 Voi.. II. 



sents several modifications of structure, which are found 

 to be characteristic of several groups, into which this 

 numerous family may be divided. In some it is thickish, 

 and more or less shelly ; in others it is thin and horny. 

 The animals of this extensive family, numbering be- 

 tween four hundred and five hundred species, are either 

 found in the humid parts of tropical forests, some 

 concealed amongst the debris at the roots of trees, 

 others creeping on the branches and foliage, or they 

 are met with in dry and arid situations, among loose 

 stones and leaves, in chalky regions. The shells aic 

 usually turbinate, and are generally covered with an 

 epidermis, which is often mottled or variegated with a 

 reddish-brown colour. The form of the shell presents 

 many modifications, as well as the operculum, and the 

 two together aflTord valuable aids in grouping the various 

 species. 



Family— HELICINIDiE {Oligyradve). 



This family consists of terrestrial, air-breathing, 

 operculated shells, like the preceding family, Cyclos- 

 tomidce. The animals scarcely difier at all in structure 

 from, and in their habits they are very similar to, those 

 of that family. The shells difler chiefly in their aper- 

 ture being scmilunate, and in the operculum not being 

 spiral. In some this operculum is thick and shelly, in 

 others thin and homy. In common with several other 

 moUusks, the Ilelicinidse possess the power of absorbing 

 the columella and the internal divisions between the 

 upper whirls. 



The genus IIelicina has a membranaceous or shelly 

 operculum, and a turbinate, globose, or depressed shell, 

 with a triangular or semi-ovate, entire aperture, and a 

 callous base. The species, which are numerous, are 

 chiefly natives of the West Indian islands and tropical 

 America, a few also being found in the Philippine and 

 Pacific islands. 



The two preceding families, as we have said above, 

 are terrestiial in their habits. The three following are 

 what may be called amphibious in their manner of 

 hfe. The respiratory organs, or gills, are disposed in 

 very numerous cross folds on the inner surface of the 

 mantle. 



Family— LITTORINID^ {Periwinkles). 



The family of Periwinkles have a spiral, turbinated, 

 or depressed shell, with a rounded, entire aperture, 

 never pearly within. The operculum is horny, spiral, 

 of few whirls. The animals possess two gills, one of 

 them very large, occupying nearly the whole surface 

 of the bronchial cavity, and formed of numerous flat, 

 free plates. 



Genus Littorina. — This genus has a thick shell, 

 pointed, and composed of only a few whirls. The axis 

 is imperforate, and the apertures subcircular and entire. 

 The columella is rather flattened, and the outer lip 

 acute. The animals have a very long tongue, thatof ihe 

 Common Periwinkle {L. lUtorca) being two inches in 

 length. The species are numerous, upwards of forty 

 having been described, and they are found on the sea- 

 shore in all parts of the world. They are amphibious 



2U 



