﻿30 PLEISTOCENE MAMMALIA. 



5. The crown of m. 3 is usually more angular The crown of m. 3 is usually less angular behind 

 behind than in U. horribilis. There is usually than in U. arctos. In teeth of the typical 

 no sinus or constriction on the outer border. triangular form there is no sulcus on the outer 

 The grinding surface presents a few coarse border. When the tooth is more elongated it 

 folds, but is never tuberculated in the slightest presents a shallow sinus dividing the outer 

 degree (Busk). border. The grinding surface is coarsely ridged, 



rarely tuberculated (Busk). 



6. The jugal arcade is more circular (Busk and The jugal arcade is more elliptical (Busk and 

 Adams). Adams). 



7. The posterior nai'ial openings are wide (Busk The posterior narial openings are of medium 



and Adams). width (Busk and Adams). 



8. The angular crotchet is less thick and incurved The angular crotchet is thicker and more incurved 



than in U. horribilis (Busk). The coronoid than in U. arctos (Busk). The coronoid pro- 



process is rather less broad and high (Owen). cess is rather broader and higher (Owen). 



9. The claws are less long and straight The claws are longer and straighter (Merriam). 

 (Merriam) . 



The constancy and importance of the above supposed distinctions may now be 

 considered. 



(1) The differences to which Busk refers are very slight, and so far as my 

 own observation goes, quite inconstant and unreliable. 



(2) The skulls of U. horribilis in the Zoological Department of the British 

 Museum do not show any marked projection of the cingulum at the antero-internal 

 corner of pm. 4 , or that the tooth tends to be shorter than in U. arctos. 



(3) Busk considered that the relative length of the interspace between c. and 

 pm. 4 , on which Owen laid stress, was not constant. This is also shown by the 

 measurements in the table on p. 11. 



(4) Nearly all palaeontologists have laid stress on the structure of pm. 4, this 

 being specially the case with Busk. Lydekker considered that Busk attached undue 

 importance to the structure of the talon. Brown, too, remarks ' that two skulls of 

 U. horribilis in the British Museum do not possess the longitudinal ridges con- 

 sidered by Busk to be characteristic of pm. 4 in this animal, while on the other 

 hand a skull of the Isabelline bear, a variety of U. arctos, possesses them. 



(6) The elliptical character of the jugal arcade is variable. In the case of two 

 grizzly bear skulls in the College of Surgeons' Museum, in No. 856, the jugal 

 arcade is more elliptical than in the brown bear skull No. 836, while in the grizzly 

 bear skull No. 854 it is not more elliptical. The skull from Ballymahon in the 

 British Museum, attributed by Adams to the grizzly bear, has the jugal arcade not 

 more elliptical than the brown bear skull No. 2 18 e in the British Museum. 



(7) It is generally the fact that the posterior narial opening is wider in the 



