98 MIOCENE FAUNA. 



The Pyramidellce and Sigareti are less numerous. Of the 

 latter genus one species, which is very rare in the Molasse (S. 

 haliotoideus, Linn.), is still living in the Mediterranean, whilst 

 a second species, which was then plentiful (S. clathratus, Rec.), 

 is now extinct. 



The species of the families Phyllidiacea and Calyptrseacea are 

 now met with everywhere on the sea-coasts, where they cling to 

 stones and rocks. The limpets (Patella) occur in the oldest 

 formations, and also inhabited the Swiss Jurassic sea (vol. i. 

 p. 136) ; one species (P. helvetica, May.) is tolerably abundant 

 in the Shell-sandstone. The very similar Fissurella (key-hole 

 limpets) and the Capuli are represented in the Molasse by two 

 species; Calyptraa includes four, and Crepidula one species. 

 The last (C. unguiformis, Lam.) clings to the rocks, with its thin 

 shell fitting all their irregularities. It is still living not only in 

 the North Atlantic and Mediterranean, but also in Africa and 

 India, and is even met with on the coasts of New Zealand, 

 proving that the magnitude of the area of distribution bears a 

 relation to the antiquity of the species. 



The toothshells (Dentaliidse) are peculiar nearly straight tubes 

 open at both ends. The genus Dentalium makes its first ap- 

 pearance as early as the Carboniferous period, and has continued 

 to the present day. Five species are preserved in the Molasse ; 

 and two of these (Dentalium incrassatum^ Sow., and D. entalis, 

 Gm.) are still met with living in European seas, whilst the 

 other three (D. fossile, Gm., D. mvtabile, Db'd., and D. Miche- 

 lottii, Horn.) became extinct in Pliocene times. 



In the marine bivalves the same conditions are repeated which 

 have been seen to prevail with the univalves, only the bivalves 

 have in general a wider distribution both in time and space. 

 Consequently more bivalves than univalves have come down to 

 recent times from the Tertiary sea ; and among them species are 

 found which are at present spread over all European seas, living 

 on the Norwegian and English coasts as well as on those of the 

 Mediterranean. The Molasse does not possess a single purely 

 fossil genus ; and, just as all the genera, without exception, have 

 continued to the present day, so many of these genera may be 

 traced back to the most remote antiquity. 



bivalves of the Molasse include species of thirty families 



