88 MIOCENE FAUNA. 



along the northern boundary of Switzerland, extending from the 

 Canton of Basle to the Randen ; and a third marine Miocene or 

 Helvetian stage. They present many peculiarities in their fauna, 

 and will therefore be described separately. 



1 . Marine Fauna of the Lowest Miocene or Tongrian Stage. 



The sea which, during the Tongrian epoch, covered the north- 

 west of Switzerland, formed a southern arm of the Alsatian 

 gulf, which was connected with the ocean that then spread over 

 northern Germany, Belgium, and the north of France. Hence 

 the Swiss fauna of the Tongrian period will be found in close 

 agreement with the fauna of that sea. In Switzerland, tip to 

 the present time, there have been collected a few polypes and 

 Polythalamia, 62 species of Mollusca *, and several Vertebrata. 

 Elsewhere 47 species of Mollusca have been found in the Ton- 

 grian stage, 31 species in the Aquitanian stage, 3 in the Shell- 

 sandstone, and 8 in the uppermost Eocene formation. The 

 greater part of the species of Mollusca are identical with those 

 of the Tongrian stage, and especially agree with the species of 

 the lowest stage of the basin of Mayence and the sands of Fon- 

 tainebleau ; many of these species also occur in the Aquitanian 

 stage in France, but very few are common to the Swiss middle 

 Miocene sea. The Swiss fauna has also only a few species in 

 common with the Eocene sea. 



All the species of Mollusca are distinct from those now exist- 

 ing ; but all the genera may now be met with in the modern seas. 

 The Cephalopoda, formerly so numerous, are wanting, and only 

 two species of Brachiopoda (Terebratula opercularis, Sow., and 

 Terebratulina polydichotoma, May.) are met with. Among the 

 univalves, the Cerithia are the most numerous, as nine species 

 of the genus occur (such as C. Boblayi, Desh., C. Lamarcki, Br., 

 C. lima, Br., C. plicatum, Lam., and C. dentatum, Desf.) ; but 



* The Mollusca of the Swiss Tertiary sea have been investigated and de- 

 scribed with great care by M. Carl Mayer. Prof. Heer is indebted to this 

 thorough student of the Mollusca of the Tertiary period for a catalogue of 

 the species discovered in the different marine stages of the Swiss Miocene, 

 which constitutes the foundation of the numerical statements given in the 

 text. 



