22 OSBORN. 



The Oligocene terminated b}- the deepening of valleys, drying of 

 the lakes and substitution of the fluviatile regime of the Lower 

 Miocene. 



Upper Oligocene 3. Aquitanien. Extensive freshwater lakes and 



lagoons. Recession of sea. 

 Middle Oligocene 2. = f Stampien. Advance of sea in Paris 



■r ) Basin. 



Lower Oligocene I. '^ \ Infra Tongrien. Marine and brackish deposits, 



lacustrine and marine Marls. 



1. Infra Tongrien, Lowier Oligocene 



Ron/.on was considered of Stampien age by Lapparent ('85, 

 p. 1 176); it is true the beds overlie the Calcairc dc la Brie, 

 Avhich is undoubtedly lower Oligocene ; Gaudry accordingly 

 places it in the Infra Tongnen, and its fauna certainly succeeds 

 closely that of the Gypsc. 



In 1 88 1, M. FiLHOL ('81, pp. 356-263) concluded that Koiicoii, 

 even after 30 years of exploration, could not be considered a 

 locality typical of the French fauna of the period. Since 1881, 

 however, considerable additions have been made to the Ronzon, 

 fauna, so that now it must be considered fairly typical (see 

 SCHLOSSER, '90). 



The animals which make their first appearance here are the 

 anthracotheres {Anthracothcriiiui said to be absent in Ronzon), 

 the elotheres, Entclodoii (Elotherium) and the rhinoceroses, 

 Ronzothcrhnn (Aceratherium), two new genera of dogs, AmpJn- 

 cynodoii and Cynodon. Otherwise the fauna continues an evolu- 

 tion of that of the Gypsc, being especially di.stinguished as the 

 last stage in which the PalceotJicriidce and the creodont Hyceno- 

 dontidce occur. 



The marsupials are represented by Pcratlicrium. Insectivores 

 are represented by Tctracits. Among rodents we find repre- 

 sentatives of the Anonialiiridce and JSIuridcE. 



The European parallels with the Mamies ct Calcairc s dc Ron- 

 zon (100 metres) fauna are mainly the newer portion of the 

 Phosphorites. If M. F'^ilhol's identification is correct in 

 establishing the three genera, Leptonianis, Nccroniaiiis and 

 Paheorycteropus, Filhol ('93, p. 129), it is possible that during 



