1911] The Ottawa Naturalist. 25 



It approaches closest to A. simum, Cope*, from which, however, 

 it differs in general proportions as well as in a number of par- 

 ticulars. 



In general shape it is broader throughout, except axially, 

 behind the hard palate and including the brain case and forehead, 

 where it is narrower; its height in its posterior half is less. 



Comparing the Yukon skull further with the Californian one 

 the following differences are apparent : (1) The breadth across 

 the maxillae, over the swelling for the root of the canine and in 

 line with the median foramen in the palate, is greater. (2) The 

 breadth across the postorbital processes is less. (3) The brain 

 case is smaller, causing a more rapid contraction of the upper 

 portion of the skull backward from the postorbital processes; 

 the narrowness is here accentuated by the greater height and 

 farther backward extension of the sagittal crest. (4) The molar- 

 premolar series occupy a shorter space. The molars and fourth 

 premolar are smaller, and the premolars in advance of the fourth 

 are less crowded. (5) The median anterior foramen, as also the 

 posterior palatine foramina occupy more posterior positions 

 relative to the teeth. (6) The posterior nares is farther back 

 from the second molar, although the hard palate apparently 

 has the same proportionate length. The posterior narial opening 

 is narrower and more pointed in front. (7) The breadth across 

 the palatines at the posterior nares is much less. (8) The breadth 

 across the mastoid processes of the periotics is much greater. 

 (9) The occipital condyles are narrower and, as seen from below, 

 their anterior margins are almost at right angles to the longi- 

 tudinal axis of the skull, and are not directed obliquely backward 

 as in A. simum. 



The following measurements of the Californian skull, as 

 given by Cope, are: 



Mm. 

 Length along base from below apex of inion to 



premaxillary 387 



The same in .4. yukonense 506 



Elevation of forehead vertically above the posterior 



extremity of the last molar 141 



The same in A. yukonense (estimated) 200 



Width between inner border of posterior molars. . . 76 

 The same in A . yukonense 93 



A. yukonense exceeded in size the largest of the living bears, 

 viz. : the Kadiak or Alaska Peninsula bear (Ursus middendorffi) 

 described by Merriam in his Preliminary Synopsis of the American 



The American Naturalist, 1S79, vol. XIII p. 791 and 800; 1891, 

 vol. XXV, p. 997, pi. XXI, figs. 1, 2 and 3. 



