18 



The Ottawa Naturalist 



[April 



(much worn) , and Ovis montana (slightly worn) are here given: 



Rock Creek Ovibos Ovis 



tooth. moschatus. montana. 



Height or length of tooth 54 mm. Ap. 40 mm. 55 mm. 



Maximum anteroposterior dia- 

 meter at grinding surface 25 mm. 31 mm. 18 mm. 



Same at mid-height _ 29 mm. 25 mm. 



Transverse diameter (width) of 

 posterior lobe at grinding 



surface 10 mm. 12 min. 6 mm. 



Same at mid-height 13.5 mm. 11 mm. 



Transverse diameter (width) of 

 anterior lobe at grinding svir- 



face. 12 mm. 13 irnn. 9 mm. 



Same at mid-height 15.5 mm. 12.5 mm. 



In attempting, therefore, to determine whether the Rock 

 Creek tooth is properly referable to the musk-ox or to the moun- 

 tain sheep, the absence of the "accessory column" in the speci- 

 men does not afford any help in this particular case, and the 

 presence of the "small accessory valley" is a character belonging 

 to both animals. According to Dr. Lonnberg, "in sheep and goats 

 this 'accessory valley' seems to be less constantly developed" 

 (op.cit.,p. 712), than in many members of the Bovidffi. Depend- 

 ing principally on its size and general robustness the Rock Creek 

 tooth is provisionally referred to the musk-ox (Ovibos moschatus, 

 Zimm.),in the belief that it may have belonged to a rather small 

 individual. 



The unconsolidated gravel under which the tooth was found 

 is evidently of Pleistocene age. The enamel of the specimen 

 varies in places from deep to light bluish-grey in colour, with a 

 few irregular patches that are almost white. The dentine is of 

 a very dark brown or almost black colour, with the cement a 

 shade lighter. Dr. Reginald Daly, geologist for Canada to the 

 International Boundary Commission, who is familiar with the 

 geology of the Rock Creek district, says that the only uncon- 

 soHdated gravels occurring there are, in his judgment, of glacial 

 origin and of Pleistocene age. 



EXPLANATION OF PLATE. 



Fu, , , J Right posterior upper true molar of ruminant (Ovibos) from 

 Rock Creek, B.C.; exterior aspect. 



Figure la The same viewed from within. 



Figure 16 The grinding surface of the same viewed from below. 



Figure Ic Transverse section of the same at d, fig. 1. 



Figure 2 Transverse section at mid-height of the crown of the cor- 

 responding tooth of an adult mountain sheep {Ovis montana, Cuv.) 

 e. "Small accessory valley." 

 All the above figures are of natural size. 



