OF WESTERN NORTH AMERICA. 



63 



contains chiefly the Plains fauna, while the irregular " Metamynodon 

 sandstones/' traversing the lower Oreodon zone and of river-channel 

 origin, contain chiefly the forest and aquatic fauna. (See fig. 9.) 

 Forested, fluviatile, and plains or open-country conditions are indi- 

 cated by the mingling of many mammals of modern type in the 

 respective fluviatile and plains deposits. 



Among Insectivora the first North American erinaceid (Proterix) 

 appears.' Rodentia include 16 genera; we note the last appearance 

 of the Eocene Ischyromyidse and the first appearance of the modern 

 Muridse. Of Carnivora-Canidae, Cynodidis and DapJidenus continue 

 from the underlying Titanotherium zone; of Felidse, 3 genera of 

 Machserodontinse ; of Mustelidse, Bunsdurus. The Perissodactyla are 

 reduced to 7 families: (a) Equidae (species numerous and diversified) ; 

 (b) Tapiridse; (c) Lophiodontidse (their last appearance); (d) Amj- 

 nodontidae (their last appearance) ; (e) Rhinocerotidae (including 

 2 genera); (/) Hyracodontidae. Artiodactyla include 8 families: 

 (a) Leptochoeridae ; (b) Elotheriidae ; (c) Dicotylidae; (d) Agriochoe- 

 ridae; (e) Oreodontidae; (/) Camelidae; (g) Anthracotheriidae ; (h) 

 Hypertragulidae. 



UPPER OLIGOCENE, FIRST PHASE. 



10. UPPER PART OF BRULE CLAY; LEPTAUCHENIA ZONE AND "PROTOCERAS 



SANDSTONES." 



(Figs. 1, 9, 10; Pis. I-III.) 



HOMOTAXIS. 



North America. — 1, Horizon C of the Hayden and Leidy section. 

 2, Upper part of White River formation of South Dakota. 3, Brule 

 clay (upper part) of Darton," 1897. LeptaucJienia zone of Wortman. 

 The '^Protoceras sandstones" contain the forest and fluviatile fauna; 

 the clays of the LeptaucJienia zone contain the plains fauna. 4, 

 Lower part of "Martin Canyon beds" of Matthew,^ northeastern 

 Colorado. 5, Deposits at White Buttes, North Dakota. 



FAUNA.'' 



Characterized negatively, so far as we know, by disappearance or 

 absence of the Hyaenodontidae, the last of the archaic Mammalia; by 

 extinction or absence of the Eocene Rodentia-Ischyromyidae ; by 

 extinction of 2 families of Perissodactyla, Lophiodontidae and 

 Amynodontidae . 



a Prof. Paper U. S. Geol. Survey No. 32, 1905. 



b Fossil mammals of the Tertiary of northeastern Colorado: Mem. Am. Mus. Nat. Hist., vol. 1, pt. 7, 

 1901, pp. 353-447. 

 c See Appendix, p. 91. 



