4 MIOCENE FAUNA. 



atilis, Linn., and Paludina tentaculata, Linn.) still exist in the 

 Swiss fresh waters ; but the other species are extinct. 



Among the bivalves the largest and most abundant species is 

 the Unio undatus, Humb., which ranges from the Aquitanian 

 stage up to the CEningian stage, and is most nearly allied to an 

 American species ( Unio rugosus. Lea) . Of the numerous loca- 

 lities in which this shell occurs we mention the following parti- 

 cularly, because they belong to various stages of the Swiss Mio- 

 cene : Brullee above Lutry, Riidholz near Soleure, Kiittigen 

 near Aarau, Dettinghofen near Eglisau, Sitterwald in the Can- 

 ton of St. Gall, Stein, Berlingen, Steckborn, and Wangen near 

 (Eningen. The freshwater mussels (Unionidce) have hitherto 

 been found only in the Upper Miocene. One species (Anodonta 

 Lavateri, Munst., sp.) occurs in great quantities in one of the 

 beds at (Eningen. It has also been found in the marls of the 

 Schrotzburg, where a smaller, broader, and more obtusely 

 rounded species (A. Heerii, May.) is met with. The latter has 

 been observed near Spreiteiibach. In the same locality of the 

 Schrotzburg Prof. Heer has found an elegant new Cyclas (C. 

 Escherij May., fig. 199), which is nearly allied to a living spe- 

 cies (C. lacmtris). 



Of the univalve Mollusca the pond-snails and mud-snails are 

 most abundant. They are sometimes accumulated in enormous 

 masses, but are generally crushed quite flat. Of the turreted 

 mud-snails (Limnaus) the most frequent species \sL.pachygaster, 

 Thorn, (fig. 198), which occurs in the Lower Miocene, near 

 Rufi in the Helvetian stage, and in the QEningian stage near 

 Zurich, Veltheim, Steckborn, and (Eningen. It is most nearly 

 allied to a species living in the Ganges (Limn&us amygdalwn, 

 Trosch.). 



Of the flat pond-snails about half a dozen species occur, of 

 which the large Planorbis solidus, Thorn, (fig. 203), is the most 

 generally distributed ; it is found in the vicinity of Zurich (near 

 Schwamendingen, at the Ealetschen, and in the Stockentobel), 

 near Kapfnach, in the Turbenthal, near Steckborn, &c. The 

 nearest ally of this species is the West-Indian and Mexican 

 Planorbis tumidus, Linn. Another species, from Delsberg and 

 Locle (P. declivis, A. Br.), most nearly resembles a South- 

 American shell (the Planorbis kermatoides, D'Orb.). 



