Paludina vivipara without food for three months, submitted them in their enfeebled state to a temperature of 23° F., and on dissolving their icy prisons he found them all living. He in a like manner experimented with Anodon cygneus with similar results.

PALUDINA LISTERI (Pl. IV., fig. 27) differs from P. vivipara in its shell being thinner and shorter, the whorls more inflated or swollen, and the sutures consequently deeper, the mouth more circular, and the umbilicus more distinct. It is usually somewhat larger.

This species is generally associated with the last, but is not of such frequent occurrence.

The shells of this species collected from a pond on Hampstead Heath, London, have their apices eroded, which is due to the action of sulphuretted hydrogen given off from the decomposing animal and vegetable matters.

The animal is very sluggish, and on being touched generally falls off the body upon which it may be crawling. The female in the autumn contains from twenty to thirty eggs, and the young are excluded at the end of two months.

GENUS BITHINIA.

BITHINIA TENTACULATA—(the Tentacled Bithinia) (Pl. III., fig. 14)-is a very common species on aquatic plants in streams, ditches, and canals

throughout Great Britain. The shell is ovately conical, of a yellowish horn-colour, smooth and semi-transparent, very frequently incrusted with a green confervoid growth. There are five or six whorls, the last one large; aperture oval, angular behind, the shelly operculum closely fitting the aperture, no umbilicus. Shell half-inch long, three-tenths wide. The animal is blackish, speckled with golden-yellow dots; the foot is lobed in front, narrow and rounded behind; the tentacles long and slender; eyes black, large, and sessile. Bouchard says that Bithinias deposit their eggs on stones and aquatic plants; the female lays from thirty to seventy eggs in a band of three rows, cleaning the surface as she proceeds; the young are hatched in three or four weeks, and attain their full growth in the second year.

BITHINIA LEACHII (Pl. III., fig. 13), named after Dr. Leach, one of the earliest systematic writers on English zoology. The shell of this species is much smaller than that of the last, being about a quarter of an inch long and two lines broad; the whorls are more swollen and rounded, distinctly separated by a deep suture; the aperture is nearly circular, and there is a small umbilicus. It is found in the same habitats as the last, but is local and less abundant, and is confined more to the southern and middle counties of England.

It can live in slightly brackish waters under tidal influence, as along the banks of the Thames below London. Dr. Gray says that the eggs are disposed on a tough strap-shaped green membrane, in a double row, consisting of six or seven pairs; the whole is fixed to the under side of aquatic plants.

GENUS VALVATA.

The

VALVATA PISCINALIS-(the Stream Valve-shell) (Pl. II., fig. 5), so named from inhabiting fishponds. The shell of this species is readily distinguished; it is globular, of four rounded well-defined whorls; colour brownish-yellow, very finely ridged, in a spiral direction; aperture circular, united all round, with a thin greyish-white operculum; there is a deep central umbilicus. Length onefourth of an inch, and as much broad. shell is very variable in the degree of elevation of the spire, and consequently in its diameter relatively to its height. The lingual ribbon of V. piscinalis is long; the central tooth (a, fig. 8) is subquadrate, with a produced base; hooked and denticulated; the three uncini (b, c, b) are lan

Fig. 8.-Teeth of V. piscinalis (Lovèn).

ceolate, and toothed on each side. A common

and widely-distributed species, very abundant on the bottoms of shallow muddy streams, on marsh lands, or on aquatic plants in ditches and canals.

Mr. Benson some years since favoured me with what appeared to be a shell of this species; but, strange to say, it was the house of a South American species of caddis-worm. The domicile was a perfect.imitation of the shell of our little V. piscinalis, and of the same size. The materials of which it is constructed are not the less singular. The spiral valvata-like tube was of the ordinary secreted matter, to which were affixed remarkably fine grains of sand; and for an operculum the scale of a fish was ingeniously appropriated.

VALVATA CRISTATA-(the Crested Valve-shell) (Pl. II., fig. 6)—is a minute species, living on the aquatic vegetation of lakes, ponds, canals, and ditches; and though it is widely diffused throughout our islands, is by no means a common species. The shell is flat, like that of a Planorbis, but easily distinguished from it by the continuous margin of the aperture, being circular, like that of V. piscinalis, for which it could never be mistaken; for in all stages of growth the shell of this species is flat above, whereas that of V. piscinalis is more or less globular. The shell is only one-tenth of an

inch in diameter, and is of a pale horn-colour, finely striated transversely, with three whorls.

The animal of this handsomely-formed species (Pl. XI., fig. 143), like that of V. piscinalis, has a plume-like gill, furnished with about fifteen branches on each side, which is usually partially protruded on the right side when the animal is crawling; on the same side of the animal there is an accessory respiratory organ, in the form of a filament, arising from the mantle: in the present species this appendage is rather shorter than the tentacles, which it so much resembles; its position, however, will not allow us to regard it as one.

FAMILY NERITIDE.

GENUS NERITINA, diminutive of Nerita, a sea-snail.

NERITINA FLUVIATILIS (the River Neritine) (Pl. IV., fig. 28)-is the only British representative of the large family Neritide of tropical seas and rivers, characterized by a thick semiglobular shell. The species of Neritina are more especially confined to rivers, and have small globular shells, coloured by bands or spots, and furnished with shelly opercula. The pretty speckled species found abundantly in many of the English rivers adhering to stones and to other shells, is about three