1 882.] Central Region of the United States. 193 



new name has also the disadvantage of being already in use for a 

 horizon of the Cretaceous, which is well distinguished palaeon- 

 tologically. 



Some genera of Rodentia are common to this formation and 

 'the White River (Steneofiber, Paheolagus ) y but its fauna is well 

 distinguished by the presence of Camelidce with a cannon bone, 

 three-toed horses with cementum in the molars, Antelope with a 

 burr of the horns (Cosoryx) and Mastodon. 



I have divided the Loup River formation into two divisions on 

 palaeontological grounds, 1 under the names of the Ticholeptus bed, 

 and the Procamelus bed. The former occurs in the valley of Deep 

 river, Montana, on the White river in Northern Nebraska, and in 

 Western Nebraska, where it has been found by Mr. Hill. Its 

 fauna presents, in Montana, a mixture of fossils of the Procamelus 

 horizon; while in Nebraska, according to Hayden, its typical 

 genera are accompanied by White river Mammalia. In the for- 

 mer region, Ihppotherium, Protohippus and Bfastomcryx are min-. 

 gled with genera allied to- Leptauchcma and with Mciycochcrrus. 

 In Nebraska, Leptauchenia is said to be accompanied by Ischyro- 

 mys, Palceolagus, Hyracodon and even Oreodon, genera which do 

 not extend to the Procamelus bed. There is, however, a question 

 in my mind whether this collocation is entirely correct. It is bed 

 D of I layden's section in Leidy's Extinct Fauna, Dakota and 

 Nebraska, p. 20. 



The material of the Ticholeptus horizon is a more or less friable 

 argillaceous sand; not so coarse and gritty as the Procamelus bed, 

 nor so calcareo-argillaceous as the White River. 



The Procamelus bed is extensively distributed. It is found in 

 Kansas, Nebraska, Colorado, New Mexico, Utah, Nevada and 

 Oregon. 



THE EQUUS BEDS. 



I can give little information respecting the depth and strati- 

 graphy of the beds of this period as they occur on the plains 

 west of the Mississippi river, for although sections of them as they 

 occur in Nebraska and elsewhere have doubtless been published 

 by authors, their palaeontological status has not been determined 

 for the localities described. My own knowledge of the deposits 

 is based on localities in California and Oregon. In Nebraska they 

 have probably been confounded with the Loup Fork beds. They 



1 Bull. U. S. Geol. Surv. Tens., V, pp. 50-52. 



