University of California Publications in Geology 



[Vol. 10 



equally rich in species, and at least in the northern hemisphere as 

 widely distributed, as during the Jurassic. One knows of finds at a 

 number of places in Germany, Switzerland, Italy, Austria, Rouma- 

 nian England, Spitsbergen, arctic and western North America, and 

 possibly New Zealand. Among these many finds there are, however, 

 only a few that have given any, palaeontologically, more enlightening 

 material. Tbe richest and most important have been the finds in the 

 Daonella limestone, in the West Humboldt Range in Nevada, of Middle 

 Triassic age ; and in California, in the Hosselkus limestone, of Keuper 

 age. 10 



The occurrence in northern Italy and Switzerland, just southeast 

 of the southern extremity of Lake Lugano, generally known under the 

 name of Besano, has been productive since the fourth decade of the 

 nineteenth century, and was, though hardly yet fully appreciated, for 

 a long time the only source of knowledge regarding the structure of 

 the Triassic ichthyosaurians. These occurrences belong to a lower 

 horizon of Keuper, Raibl-St. Cassian. 1 



The German occurrences have hitherto yielded little, but recently 

 a new find has been made, and the material scattered in various mu- 

 seums has been brought together, so that von Huene 7 has been able to 

 show that twenty species, representing seven genera, are to be found. 

 Of these, however, only eight species are sufficiently represented to 

 make it possible for them to be named. Of the seven genera six are 

 represented in other species from California, Nevada, Spitsbergen, 

 and Besano. The whole of the material seems to come from the 

 Muschelkalk. 



The Spitzbergen Trias vertebrates are, with a few exceptions, dis- 

 tributed in four horizons. If the lowest, the first horizon, is fixed at 

 zero, they lie at something like the following distances from each other : 



The new vertebrate horizon 360 ? m. 



The upper saurian horizon 205-210 



With regard to stratigraphy in general, reference is made to the 

 work by Nathorst. 16 Above the arenaceous beds, belonging presum- 

 ably to the Buntsandstein,-" which were previously referred to the 

 Permian, come the Posidonomya slates. Near the base of these lies 

 the fish horizon, and somewhat deeper than that part of the layer 

 which from older Swedish ammonite finds was known to Mojsisovics. 15 

 Probably the lower saurian horizon also comes within this layer. 



The lower saurian horizon 

 The fish horizon 



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