UNIVALVES. 97 



the Swiss Jurassic sea (vol. i. p. 136) ; and seven species of these 

 genera appear in the Miocene, six of them belonging to the 

 genus Trochus, which is distributed through all seas, whilst 

 Turbo chiefly inhabits the torrid zone. A similar remark may 

 be made of the Turrit elite, thirteen species of which inhabited 

 the Swiss Molassic sea. These are all extinct species, several 

 of which (such as T. turns and T. Archimedis) received a screw- 

 like appearance from the spiral twisting of the angles of their 

 long turriform shells. The genus Xenophora is remarkable for 

 the numerous shell-valves which the animal affixes to the whorls 

 of its shell, which thus acquires a singularly ragged appearance. 

 Switzerland has two species, one of which (X. turicensis, May.) 

 is tolerably abundant in the Shell-sandstone, while the other (X. 

 Deshayesi, Mich.) occurs in the subalpine Molasse. Of Mono- 

 donta we have a Mediterranean species (M. Aaronis, Desh.) ; of 

 Adeorbis one, and of Solarium two extinct forms (S. carocolla- 

 tum and simplex) occur. 



The family Scalariidae receives its name from the shells of the 

 animals composing it being twisted in a long spiral, sometimes 

 almost tubular, with a round aperture. The genus Delphinula, 

 which lives in the seas of warm climates, possesses only one 

 species (D. helvetica, May.) in the Molasse. Scalaria, which is 

 distributed in all seas, has four species. The worm-shells, which 

 are furnished with tubular shells like those of the Tubicolar 

 Annelides, are represented by two species ( Vermetus arenarius 

 and V. intortus, Lam.) still living in the Mediterranean, and the 

 very similar Siliquarice by one species (S. anguina, Linn.), which 

 is now met with both in the Mediterranean and in Indian 

 seas. 



Among the Plicacese, Natica forms a genus already known in 

 Switzerland since the Jurassic epoch (vol.i. p. 136). It has in- 

 habited the sea at all times, and extends from the icy sea to the 

 South Sea, 189 species being known from all parts of the world. 

 The species are predaceous animals, living at the bottom of the 

 sea ; they bore into other Mollusca, and bury themselves in the 

 sea-bottom. Of the nine species of the Molasse, we find four 

 living in existing seas; and three of these (N. millepunctata, 

 Linn., N. helvicina and Josephina, Risso) are confined to the 

 Mediterranean. 



VOL. II. H 



