PHYLUJXViii VERTEBRATA 113 



extremely rare, while the Physostomi constitute about three-quarters of all 

 the known species. The Physoclysti, like the Physostomi, are represented 

 chiefly by extinct genera. 



With the beginning of the Tertiary period there is a still closer approxima- 

 tion to the condition of affairs at present prevailing. 



The oldest Eocene fish fauna of Europe, from the London Clay of southern 

 England, is incompletely investigated. The contempoi'aneous deposits in the 

 Paris Basin yield only a few fish remains, but among these are scales of the 

 Ganoid genus Lepidosteus, which still exists in North America. The most 

 important and best known deposit of Eocene fishes is the light-coloured fissile 

 limestone of Monte Bolca, near Verona, which corresponds in age approxi- 

 mately with the Calcaire Grossier of the Paris Basin. No less than 94 genera 

 and 170 species, including several sharks and rays, have been described from 

 it. Of Ganoids only the Pycnodonts here survive; all the other fishes belong 

 to the Teleostei, most of them indeed to genera which at present live in the 

 Indo-Pacific and Eed Sea, in the tropical Atlantic, and to a smaller degree 

 also in the Mediterranean. The most interesting feature in this fauna is the 

 great increase of the Acanthopteri and the decrease of the Physostomi. 



A remarkable fish horizon, partly marked by deep-sea fishes, occurs at the 

 summit of the Eocene, represented in the black slates of Matt in Canton 

 Glarus, the contemporary Menilite Shales of Styria, Upper Bavaria 

 (Siegsdorf), Upper Alsace, and other localities. From Glarus, the richest 

 locality for this zone, 29 species of fishes are known, according to Wettstein, 

 and all of these belong to the Teleostei. In a remarkable way the extinct 

 genera here considerably exceed those which survive to the present day. 



In the western states of North America, in the so-called Puerco, Wasatch, 

 and Bridger formations of New Mexico and Wyoming, fossil fishes are also 

 abundant ; but these, since they occur in freshwater deposits, have little in 

 common with the Eocene forms of Europe, which are met with almost 

 exclusively in marine or estuarine deposits. It is interesting to note that the 

 existing North American Ganoid families, Lepidosteidae and Amiidae, are 

 represented here. 



The Oligocene and Lower Miocene yield but scanty fish remains. The 

 occurrence in Europe of Amia {Notaeus) and Lepidosteiis is noteworthy. 



The Middle Miocene Molasse of Switzerland, Swabia (Baltringen), and 

 Upper Bavaria, the marine deposits of the Vienna basin, the valley of the 

 Rhine, and the Aquitaine basin sometimes contain an abundance of fish 

 remains, among which the teeth, dermal plates, and spines of sharks, rays, and 

 chimaeras, the vertebrae, teeth, and scattered bones of Teleostei are especially 

 common. With few exceptions these remains are referable to recent genera. 

 The brackish-water clay of Unterkirchberg, near Ulm, the freshwater marl of 

 Oeningen and Steinheim, the Sarmatian deposits of Radoboj and other localities 

 in Croatia, and the Cerithium marl of the Vienna basin, also show that at the 

 time of their foi"mation the fish fauna of the fresh and brackish waters of 

 Germany was not very different from that still surviving in southern Europe 

 and Asia Minor. 



The remarkably rich Upper Miocene fauna of Licata in Sicily exhibits a 

 mixture of marine and freshwater fish remains, which is also partially notice- 

 able in the neighbourhood of Girgenti, in the gypseous marls of Sinigaglia, 

 near Gabbro in Tuscany, Lorca in Spain, and Oran in Algeria. In his mono- 

 VOL. II I 



