SUB-ORDER B PLATYPODA 463 
Omphalopterus, Roem. Depressed turbinate, widely umbilicate. The wide peri- 
pheral margin at the base composed of two lamellae, 
separated by a slit. Silurian. 
Clisospira, Billings; Autodetus, Lindstrom. Silurian. 
Xenophora, Fischer (Phorus, Montf.), (Fig. 900). Low 
trochiform, narrowly umbilicate. Whorls usually covered 
above with agglutinated extraneous objects. Cretaceous to 
Recent. 
Family 7. Ampullariidae. Gray. 

This family inhabits fresh or brackish water, and. is 
found in Africa, Asia, and tropical America. Some-of — xenophora agglutinans, Lam. 
their shells are hardly to be distinguished from Natzca. poe Grossier ; Damery, near 
The animal possesses a lung cavity above the right gill. ee 
Fossil forms occur in freshwater deposits of Cretaceous age at Rognac, near Marseilles, 
and also in the early Tertiary. 
Fra. 900. 
Family 8. Valvatidae. Gray. 
Shell composed of few whorls, conical or discoidal, wmbilicate. Aperture round, with 
continuous peristome. Operculum horny, circular, multispiral. 
Upper Jura to Recent. 
The genus Valvata, Mull. (Fig. 901), is small, and varies 
from turbinate to discoidal. It comprises about twenty-five 
recent species, inhabiting the fresh waters of Europe and North 
America. It is initiated in the Purbeck, but does not become 
at all abundant until the Tertiary. 

Fic. 901. 
Valvata piscinalis, Mull. 
Upper Miocene; Vargas, 
Transylvania. 
Family 9. Viviparidae. Gill. 
Shell conical or turbinate, with thick epidermis; tmperforate or with narrow 
umbilicus. Whorls smooth, tubular or angular. Aperture rounded, oval, sub-angular 
posteriorly, with continuous peristome. Operculum horny, concentrically striated, with 
eccentric nucleus. Jura to Recent. 
Viviparus, Montt. (Paludina, Lam.), (Fig. 902). This, the principal genus, is 
abundant in fresh water of all parts of the globe, with the exception of tropical and 
South America. Several 
other genera and sub- 
genera are recognised, 
such as Campeloma, Raf. 
(Melantho, auct.), of 
North America, compris- 
ing mostly smooth, thick- 
shelled species, with 
thickened inner lip; 
Tulotoma, Haldem., in- Fre. '608: 
cluding forms with an- A, B, Viviparus Brusinae, Neumayr. C, V. (Tulotoma) Forbesi, Neumayr. 
gular whorls, North Pliocene 3 Isle of Cos. D, V. (Tulotoma) Hoerneri, Neumayr. Pliocene ; 
ements . Margarya, Noyska, Slavonia. 
Ney., China; Lvioplax, Troschel; Laguneula, Benson; Tylopoma, Boskovicia, 
Brusina, ete. 
Typical species of this genus are found in the Wealden clays. Vast numbers of 
Viviparus occur in the Pliocene of Southern Hungary, Croatia, Slavonia, Roumania, 

