22 ■ OSBORN. 



The Oligocene terminated b)^ the deepening of \'alle}'s, 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. 

 Stampien. Advance of sea in Paris 



Basin. 



Lower Oligocene l. '^ ] Infra Tongrien. Marine and brackish deposits, 



i2 lacustrine and marine Claris. 



Middle Oligocene 2. 



1. Infra Tongrien, Lower Oligocene 



Ronzon was considered of Stampien age by Lapparent ('85, 

 p. 11/6); it is true the beds overHe the Calcairc dc la Brie, 

 which is undoubtedly lower Oligocene ; Gaudry accordingly 

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

 closely that of the Gypsc. 



In 188 1, M. FiLHOL ('81, pp. 256-263) concluded that Ronzon, 

 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 (AntJiracotlicrinni said to be absent in Ronzon), 

 the elotheres, Entclodon (Elotherium) and the rhinoceroses, 

 RonzotJicrinni (Aceratherium), two new genera of dogs, AnipJn- 

 cynodon and Cynodon. Otherwise the fauna continues an evolu- 

 tion of that of the Gypsc, being especially distinguished as the 

 last stage in which the PalceotJicriidce and the creodont HycEno- 

 dontidce occur. 



The marsupials are represented by PcratJicriiim. Insectivores 

 are represented by Tctracns. Among rodents we find repre- 

 sentatives of the AnoniahiridcE anc^ Mnridcu. 



The European parallels with the Marncs ct Calcaircs dc Ron- 

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

 Phosphorites. If M. Filhol's identification is correct in 

 establishing the three genera, Leptonianis, Nccronianis and 

 Palceoryctcropus, Filhol ('93, p. i 29), it is possible that during 



