94 MIOCENE FAUNA. 



On examining the extinct species of the fauna of the Swiss 

 Molassic sea, it is found that among the Mollusca the Mediter- 

 ranean forms predominate, that exclusively northern forms are 

 wanting, but that, on the other hand, numerous tropical types 

 now absent from the Mediterranean occur ; so that on the whole 

 the Swiss Miocene marine fauna acquires a more southern cha- 

 racter than that of the existing Mediterranean zone. We find 

 in it genera which now pertain exclusively to tropical seas, such 

 as the splendid Volutes, the long turriform Terebra, the Nautili, 

 and the genera Oniscia, Pyrula, Ficula, Delphinula, and Tugonia, 

 with others which chiefly inhabit the tropics, and are only re- 

 presented in the Mediterranean by a few species, such as the 

 variegated Cones, the brilliant Cyprea, the genera Mitra, Cassis, 

 Cancellaria, Pleurotoma, Turritella, Turbo, and Tritonium, and 

 among bivalves Tellina, Psammobia, Cytherea, and Chama. 



On recapitulating the forms hitherto collected in Switzerland, 

 we find among the 431 species of Mollusca, 203 marine univalves 

 and 228 marine bivalves. The former belong to 15 families. 

 The Cephalopoda, which were so numerous and varied in prece- 

 ding periods, are represented by only a single species (Nautilus 

 Aturi) ; and even this is extremely rare, and has only been found 

 near Wiirenlos. Of the family Conidse, which principally belongs 



cent, of living species. In the Swiss Helvetian stage the living species con- 

 stitute 25-5 per cent, of tlie marine univalves, in the Shell-sandstone alone 

 22-6 per cent., and in the subalpine Molasse 25-7 per cent. Of the bivalves 

 there are in the Vienna basin, as in Switzerland, more living species than of 

 the univalves, so that higher percentage numbers are obtained for the whole 

 of the Mollusca. The Swiss Helvetian Molasse represents the middle and 

 upper marine beds of the Vienna basin. In the lowest bads (called " Hor- 

 ner " beds) the living species of marine univalves constitute only from 12 to 

 15 per cent. The marine beds are followed in the Vienna basin by a brackish- 

 water formation, which coincides with the Swiss CEningian stage j it passes 

 into a freshwater formation (the Congerian or " Inzerdorfer " beds), in 

 which Mastodon longirostris has been found ; whilst in the brackish-water 

 and marine beds the Mastodon tapiroides and angmtidem are met with, which 

 consequently frequented the shores of the Viennese sea, just as they did those 

 of the Helvetian sea. The Swiss Molasse has 138 marine univalves, or 68 per 

 cent., in common with the Vienna basin. Of the bivalves there are no doubt 

 a still larger number of common species. 



