39 



Hyracodon nebrascensis, Leidy. 



Aceratherium pumilum, Cope, in part, 1885. The "White River beds of Swift-current river, 

 North West Territory ; American Naturalist, vol. XIX, p. 163, name only. 



Aceratherium pumilum, Cope, 1885. Geol. and Nat. Hist. Survey of Canada, vol. I, new 

 series, part C, appendix I, p. 83, specimen II; and 1891, this volume, part I, p. 19, 

 specimen II, pi. IV, fig. 4. 



Hyracodon neb rascense, Osborn, 1898. The Extinct Rhinoceroses. Memoirs Amer. Mus. 

 Nat. Hist., vol. I, pt. Ill, p. 138, fig. 38. 



The principal specimen from the Cypress hills, representing this species, is the portion of 

 mandible, holding teeth, described by Cope under the name Gcenopus pumilus, (specimen 2). 

 This specimen, as pointed out by Osborn in 1898, is part of the right ramus of a young 

 individual of H nebrascense. A tooth, belonging to the collection 1904, is referred to this 

 species : it is from the right side of the lower jaw, and is apparently a deciduous third pre- 

 molar. 



Hyracodon priscidens, Lambe. 



Plate IV, figs. 1, 2, 3 and 4. 



Hyracodon sp., Lambe, 1905. Geol. Survey of Canada, Summary Report for 1904, p. 368. 



Hyracodon priscidens, Lambe, 1905. A new species of Hyracodon (H. priscidens) from the 

 Oligocene of the Cypress hills, Assiniboia ; Trans. Royal Soc. of Canada, second series, 

 section IV, vol. XI, p. 37, pi. I, figs. 1, la. 



Another species of Hyracodon is represented, in the collection of 1904 from the Oligocene 

 deposits at Bone coulee, Cypress hills, by an upper jaw with teeth, giving the complete pre- 

 molar-molar series. Three teeth are missing, viz., the fourth premolar from the left side, 

 and the second and third premolars from the right. As the form of the tooth in each case 

 is seen in the corresponding one of the opposite side, the details of structure of all the cheek 

 teeth are presented. The ectoloph of the right third premolar remains. The teeth are in an 

 excellent state of preservation and, as they are only slightly worn, evidently belonged to a 

 young animal. The last molar on either side has not protruded from the jaw to its fullest 

 extent. Both ju^als are preserved, and, on the right side, part of the squamosal also. 



The specimen to which the following remarks apply consists for the most part of the 

 two maxillary bones holding teeth. These bones are imperfect in their lateral upward 

 extension. The right maxilla is broken off slightly in advance of the first premolar, but, on 

 the left side, the full extent of the diastema, separating the first premolar from the canine, is 

 preserved. The lower margin of the orbital opening on either side is intact. 



This specimen (type) indicates an animal of about the size of Hyracodon nebrascensis, 

 Leidy, from the Oligocene of Nebraska, South Dakota and Colorado, from which, however, 

 judging from its tooth structure, it differed specifically. The species has been described 

 under the above name. 



Hyracodon priscidens, as compared with H nebrascensis, exhibits the following charac 

 teristics : — (1) The teeth are shorter or more brachyodont, (2) in the premolars the protoloph 

 is continued in a curve round the inner end of the metaloph, the tetartocone being confluent 

 with the deuterocone and arising from the protoloph, (3) in the last molar, m'\ the ectoloph 



