QUATERNARY FAUNA OF GIBRALTAR. 65 
As regards the lower jaw, of which we have little more than the horizontal ramus, 
the only difference that I can perceive between it and the corresponding portion in 
three mandibles of U. fossilis from the Gower caves consists in the greater thickness 
of the interior border, which is very much thinner in the Welsh specimens, the jaws 
otherwise corresponding exactly in dimensions as to vertical diameter and thickness. 
The important differential character afforded by the angular “ crochet,” which is 
thicker and more incurved in U. fossilis and ferox than in U. arctos, is unfortunately 
absent in the Gibraltar bone, as are also those derivable from the ascending ramus, 
coronoid process!, &c. 
The two remaining teeth in this mandible are rather smaller than in the Gower 
specimens, but very slightly so; and the most important of them in a comparative 
point of view, the pm. 4, is wanting, having been shed during life, and the alveolus 
wholly obliterated. This tooth, however, exists quite entire in one of the other 
specimens, and corresponds in all respects much more closely with that tooth in U. 
arctos than with that of U. fossilis. The important characters afforded by the pm. 4 
in U. speleus are very well known; and, to a less decided extent, it seems to me to 
afford one of the most important means of diagnosing U. arctos from its most closely 
allied congener. 
In studying the dental characteristics of different species of Bears, we have to regard, 
first, their size and proportions to each other, and, secondly, any differences of pattern 
they may present. With regard to the former of these points, as will be obyious from 
the odontograms (Pl. XX VII. nos. 6-10), no conclusions could in the present case be 
drawn, except that the teeth in the Gibraltar specimens are, with perhaps one ex- 
ception, fully as large as those of the existing U. ferox (No.7), or even of U. fossilis 
(No. 6), and, on the whole, somewhat larger than the largest known to me of U. arctos 
(No. 10). As regards the second point, it may be observed that, unfortunately, the 
general resemblance of most of the teeth in all the larger carnivorous Bears, as regards 
form and pattern, is so close, and moreover so liable, within certain limits, to vary 
very considerably, that but few of them are practically available for the purpose of 
drawing specific distinctions. From the circumstance, also, that a very moderate 
amount of wear destroys the more minute particularities of sculpturing, characters of 
that kind can seldom be employed with any advantage. 
For these reasons, it will generally be found sufficient to advert only to those teeth 
which afford the most marked and least readily effaceable features. These appear to be 
the second or last upper molar (m. 2), and the first and last molars of the lower jaw 
(pm. 4 and m. 3). 
The last upper molar in U. spelwus, besides its much greater size, is usually distin- 
guished by its more or less oblong form, the sides being nearly parallel, and the hinder 
Professor Owen (Brit. Fossil Mamm. p. 83) adduces the greater breadth and height of the coronoid process 
as a point of difference between U. priscus and. UV, arctos. 
