QUATERNARY FAUNA OF GIBRALTAR. 67 
In U. arctos the tooth is also triangular in form, but usually more angular behind, in 
accordance with the more pointed shape of the corresponding upper molar. It has 
usually no constriction on the outer border; and the anterior and inner cusp is generally 
but little developed. The grinding-surface presents only a few coarse folds or ruge, 
and is never, so far as I have seen, tuberculated or granulated in the slightest degree. 
‘The fourth lower premolar (pm. 4) is in some respects the most characteristic of all 
the teeth ; and were its characters rather less liable to vary by defect in U. Sossilis and 
U. ferox, it might almost by itself be considered sufficient to give assurance of the species. 
Its distinctive characters in U. speleus are well known; and when fully developed and 
unworn it seems to me to afford excellent distinctive characters also between U. Serox 
and U. arctos. 
In Ursus speleus, besides the principal cone, there are usually on the inner side two, 
and always one, smaller cusps, of which one is anterior in position to the principal cusp. 
In all other Bears this tooth has either a single conical cusp, or at most a single small 
internal tubercle posterior in position to the principal cusp, and corresponding to the 
hinder of the two internal cusps in U. speleus. 
Tn all the large carnivorous Bears this tooth presents séveral common characters, the 
differences exhibited in various species depending solely, as it would seem, upon the 
degree of development or suppression of minute parts. 
In all cases the tooth presents a large conical cusp, which is placed nearer the 
anterior than the posterior border of the crown. An acute ridge or keel, in perfectly 
unworn teeth, descends from the point of the cusp in front to the anterior end of the 
crown, where it terminates after making a slight curve inwards, in a more or less distinct 
though always very minute tubercle. Two similar but more strongly marked ridges 
descend from the apex of the cone towards the hinder border of the tooth. 
In fully developed and perfectly unworn teeth in U. fossilis, ferox, and maritimus 
(and, I have no doubt, also in U. arctos, though I have seen no tooth of that species young 
enough to show it), these hinder ridges are more or less distinctly serrated, especially the 
outer one, which is always continued to the hinder border of the tooth, whilst the 
internal ridge rarely reaches more than halfway between the base of the cone and the 
hinder border. Now the differencesin the fourth lower premolar, as between U. Sossilis, 
Jerox, and arctos, consist solely in the varying degree of development of these minute 
parts. In well-marked teeth of U. fossilis taken in the germ-condition, the anterior 
carina and the tubercle at its base are strongly developed. ‘The outer of the two 
hinder carine, which is deeply serrated, terminates at the posterior border of the crown 
in a small tubercle, on the inner side of which is placed a second tubercle of equal size ; 
so that the hinder extremity of the crown (or the talon, as it may be termed) might in 

appears to be deeply sinuated on the outer border ; but this appears to have arisen from the circumstance that 
the figure has been taken from Goldfuss’s specimen in the British Museum, in which the tooth has a 
piece chipped off at that spot. 
