The royal natural history . // toa, 388 MOLLUSCS. furnished with gills, they are more or less amphibious, passing part of their timeout of the water. Four are British. The viviparous pond-snails (Viviparidcv) in general appearance are not unlikeperiwinkles, having a longish contractile rostrum and elongate pointed tentacleswith the; eyes situated upon short projections at the base. There are two neck-lappets, the right forming a rudimentary respiratory siphon. The foot is broadin front and narrowed behind. The species of Vivipara, as their name implies,are viviparous, and the young are brought
The royal natural history . // toa, 388 MOLLUSCS. furnished with gills, they are more or less amphibious, passing part of their timeout of the water. Four are British. The viviparous pond-snails (Viviparidcv) in general appearance are not unlikeperiwinkles, having a longish contractile rostrum and elongate pointed tentacleswith the; eyes situated upon short projections at the base. There are two neck-lappets, the right forming a rudimentary respiratory siphon. The foot is broadin front and narrowed behind. The species of Vivipara, as their name implies,are viviparous, and the young are brought forth provided with a shell havingthree rows of bristles, and at once start upon an independent career, like theadult. They are sluggish creatures, and generally live more or less in mud at the. viviparous pond-snails, Vivipara; male on left, female on right, young (magnified) in front. bottom of rivers or canals, and feed upon decaying vegetable or animal North American species form the genera Melantho and Tylotoma,and most have more solid shells than in Vivipara. One of the finest speciesoccurs in Lake Tanganyika, and is remarkable on account of the aperturebeing somewhat effuse at the base, and in having the outer lip slightly sinuatedin the middle. On this account it was at one time placed in the separate genusNeothauma, but examination has shown that it does not essentially differ fromVivipara. The character of the lingual teeth in this family is shown in theaccompanying figure representing a single transverse series. Two species occurin England, one of which (V. contecta) is here figured. The Valvatidai comprisea few small molluscs closely allied to the last. They occur in Europe and NorthAmerica, and are remarkable for protruding a plume-like gill beyond the
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Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectzoology
