Section IV-, 1905. [ 37 ] Trans. R. S. C. 



III. — A new species of Hyracodon (H. priscidens) from the Oligocène 

 of the Cypress Jiills, Assiniboia. 



By Lawrence M. Lambe, F.G.S., Vertebrate Palseontologist to the 

 Geological Survey of Canada. 



(Read May 25, 1905.) 



A species of Hyracodon is represented, in the collection of 1904 

 from the Oligocène deposits at Bone coulée, Cypress hills, by the upper 

 jaw, with teeth, giving the complete premolar — 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 be- 

 longed to a young animal. The last molar on either side has not 

 protruded from the jaw to its fullest extent. Both jugals are preserved, 

 and on the right side part of the squamosal is present. 



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. 



The specimen indicates an animal of about the size of Hyracodon 

 nehrascensis, Leidy from the Oligocène of Nebraska, South Dakota 

 and Colorado, from which, however, judging from its tooth structure, it 

 differed specifically. 



The Cypress hills species, as compared with 11. nehrascensis, ex- 

 hibits the following characteristics: — (1) The teeth are shorter or more 

 brachyodont; (3) 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 is relatively much shorter with a concomitant 

 greater development of the metaloph; (4) the exterior cingulum is 

 developed only on the posterior half of the base of the ectoloph in the 

 seven teeth, and the internal cingulum is absent in p^; (5) the parastyle 

 in the premolars is only slightly developed; (6) the skull is apparently 

 flatter and relatively more elongate, the lower margin of the orbit being 

 less distant from the alveolar border, and the jugal less curved upward 



