of the white river beds of Montana. 245 



beds of pure volcanic dust in the Loup Fork of Montana. It is very likely that the 

 greater part of the deposits are a mixture of clay, fine sand and volcanic dust, with an 

 abundance of calcareous matter in some places. Often, as previously staled, there arc 

 strata of limestone. In many places this limestone contains an abundance of fresh-water 

 shells. These have not yet been specifically determined. Sometimes for a considerable 

 thickness there is no distinct stratification, and in other places there are thin layers 

 and distinct lamination. Near New Chicago, in thinly laminated shales, a few fish 

 remains were found, and a little distance away, in a harder layer, fragments of bone, 

 including part of a metapodial of an Oreodont associated with snails. 



If the beds that do not contain fossil mammals, but have the same appearance as 

 'hose that do contain them, are of the same age as (he latter, there was a large area of 

 deposition in Montana,. 



There has been considerable disturbance since the deposition of the White River 

 beds, for in some places the strata, dip at a high angle. I have not seen any distinct 

 shore markings except in the vicinity of Missoula,, where there was undoubtedly a lake 

 in Pleistocene times. 



The work on this paper has been done in the Museum of Princeton University, to 

 which the greater part of my collection lias been removed for study. It is due to the 

 broad-minded interest of Prof. W. B. Scott that I have been enabled to do the work under 

 such favorable circumstances, and his intelligent criticism has been of the greatest value 

 to me. Dr. Marcus 8. Farr, the Curator of Vertebrate Pabwontology, has given me free 

 access to the Museum and helped me in every possible way. The drawings of fossils 

 were made by Mr. F. Von Person. The map was drawn by myself. 



All the specimens described in the paper were found in Montana, by myself and they 

 are now in my collection, to which the numbers in the text refer. 



Princeton Museum, May 2, 1901. 



Descriptions of Species. 

 Ictops acutidens, sp. nov. 



The type, No. 36 of my collection, consists of portions of a skull, mandible and 

 other bones with a nearly complete femur, astragalus, calcaneum and one lumbar vertebra. 

 It was a young individual. The epiphyses are free and the last lower premolar erupting. 

 I do not know whether the last two upper premolars are permanent or temporary, but 

 will describe them as they are. 



If full grown the animal was smaller than I. dakotensis* and differs from it inseveraj 



* fV 



Compared with specimen in the American Museum of Natural History. 

 A. P. S. — VOL. XX. FF. 



