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510 GEOGRAPHICAL ZOOLOGY. [part iv
Family 12.—LITTORINID^. (9 Genera, 310 Species.)
Distribution.—The Littorinidae are mostly found on the coasts
in shallow water ; as the common Periwinkle {Littorina littorea).
They are of world-wide distribution ; but Solarium and Phorus
are tropical ; while Lacuna, Skenea, and most species of Rissoa
are Northern, About 180 species are fossil, ranging from the
Permian to the Pliocene formations.
Family 13.-PALUDINID^. (4 Genera, 217 Species.)
Distribution.—The Paludinidse, or Eiver-snails, are all fresh-
water, and range over the whole world. Paludina (60 sp.), is
confined to the Northern Hemisphere ; Amjmllaria- (136 sp.),
is tropical ; Amphihola (3 sp.), inhabits New Zealand and the
Pacific Islands ; Valvata (18 sp.), North America and Britain.
There are 72 fossil species of Paludina and Valvata, in the
Wealden formation and more recent fresh-water deposits.
Family 14.—NEPJTID^. (10 Genera, 320 Species.)
Distribution.—All warm seas, ranging north to Norway and
the Caspian Sea. Neritina and Navicella inhabit fresh or brack-
ish waters, the latter confined to the countries bordering the
Indian Ocean and the islands of the Pacific. There are 80 fossil
species, from the Trias, Lias, and Eocene formations down to
recent deposits.
Family 15.—TUEBINID^. (10 Genera, 425 Species).
Distribution.—The genus Trochus (200 sp.) has a world-wide
range, but the other genera are mostly tropical, and are most
abundant in the Indian and Pacific Oceans. There are more
than 900 fossil species, found in all parts of the world, from the
Lower Silurian to the Tertiarv formations.