. The Cambridge natural history. Zoology. ORIGIN OF FRESH-WATER UNIVALVES 17 Chem.) ascends rivers as far as 25 miles from their mouth, and others haunt marshes of brackish water. Neintina is the fresh- water form, some species of which are found in brackish swamps or even creeping on wet mud between tide marks, while the great majority are fluviatile, one group (Neritodryas) actually occurring in the Philippines on trees of some height, at a dis- tance of a quarter of a mile from any water. Navicella is a still further modified form of Neritina^ occurring only on wet rocks, branches, etc, in
. The Cambridge natural history. Zoology. ORIGIN OF FRESH-WATER UNIVALVES 17 Chem.) ascends rivers as far as 25 miles from their mouth, and others haunt marshes of brackish water. Neintina is the fresh- water form, some species of which are found in brackish swamps or even creeping on wet mud between tide marks, while the great majority are fluviatile, one group (Neritodryas) actually occurring in the Philippines on trees of some height, at a dis- tance of a quarter of a mile from any water. Navicella is a still further modified form of Neritina^ occurring only on wet rocks, branches, etc, in non-tidal streams (Fig. 13). 1. Fig. 13. â Illustrating the development of the fresh-water genus Navicella, through the brackish-water jSferltina, from the marine Nerita, with corresponding changes in the operculum. 1. Nerita; 2,3. Neritina; 4. iVertYina, intermediate form ; 5, 6. Navicella. The great family of the Melaniidae, which occurs in the rivers of Avarm countries all over the world, and that of the Pleuroceridae, which is confined to North America, are, in all probability, derived from some form or forms of Cerithium. The origin of the Paludinidae, Valvatidae, and Ampullariidae is more doubtful. Their migration from the sea was probably of an early date, since the first traces of all three appear in the lower Cretaceous, while Melaniidae are not known until Tertiary times. AmpuUaria, however, shows distinct signs of relation- ship to Watica, while the affinities of Paludina and Valvata can- not as yet be approximately affirmed. (2) Pulmonata.âIntermediate between the essentially fresh- water and the essentially marine species come the group some- times known as Gehydrophila, consisting of the two families Auriculidae and Otinidae. These may be regarded as MoUusca which, though definitely removed from all marine species by the development of a true lung or lung cavity in the place of a gill, VOL. Ill â C. Please note that these images are extracted from scanned page
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
