TERTIARY MAMMAL HORIZONS. 15 



Three perissodactyl phyla occur, namely the Hyracotherii- 

 nae, Lophiodontinas and Helaletinse, whereas at the same period 

 in America we find the Hyracotlicriincc, TapiridcE, and Hclalctincu. 



Without exception in the Lutetien representatives of the 

 perissodactyl families LophiodontincE and HyracotheriincE tJic 

 premolars arc simpler than the molars and these animals are 

 therefore in a stage of evolution corresponding with that which 

 ive find in the Wiiid River beds. The horses so far as I can 

 judge from personal study, from Filhol's descriptions and 

 from figures, (Gervais, '59) P. Snillns, P. parvulns, P. dnvalii, 

 all belong to the primitive stage, namely, premolars simpler than 

 molars, no inesostyh\ and are therefore in a Wind River {Pro- 

 torohippns) rather than Bridger iOrohippns) stage of develop- 

 ment. FiLHOL ('88, p. 182) lays great emphasis upon the fact 

 that all the so-called * Pachynolophus ' of Issel, Pepieux and 

 Lautrec have the premolars simpler than the molars. Further- 

 more in beds of undoubted Issel, Argenton or Buchszueiler age, 

 no complete Anchilophns types of premolars (pm = m) occur. 

 As for the oldest Artiodactyla in either country. Cope ('82, p. 

 71) has compared Lemoine's Lophiodochoeriis peroni of the 

 Argiles-a-lignites with his Trigonolestes brachystomns, from the 

 Wind River. Among the primates the little known Heterohytts 

 armatns Gervais, distantly resembles Alicrosyops of the Bridger 

 in its molar teeth only, the premolars being simpler than in the 

 Bridger species. 



These are significant facts. So far as they go they indicate 

 that the known beds of Lutetien formation (having a thickness of 

 45—24 metres) are by no means equivalent to the Bridger Beds 

 (having a thickness of 800 metres), as heretofore stated, but 

 they merely correspond to a section of the Lower Bridger or 

 more probably of the Upper Wind River formation. 



It is true that in the Helaletince, or cursorial Lophiodonts, in 

 the fauna of Egerkingen and Lissien, namely H. car tier i, H, 

 annectens (and perhaps Helaletes (Hyrachyus) intermedins of 

 Sclles-siir-Cher^, the third and fourth premolars have double 

 internal lobes like those of H. (pesmatotJicriiini) gnyotii of the 

 Bridger. But it must be remembered as regards both Eger- 



