66 MR. G. BUSK ON THE ANCIENT OE 



end not much narrower than the middle, and never, or scarcely ever, at all pointed. The 

 grinding-surface also, in the perfectly unworn condition, is characterized by its com- 

 parative flatness or expansion transversely. On the outer border there are three cusps, 

 the hindmost of which, however, is very low and soon worn off. Of the two larger 

 conical cusps the anterior is stronger than the posterior, which latter presents no trace 

 of an accessory intermediate tubercle in front. 



In U.ferox and U.fossilis the tooth is more contracted behind than in U. sjjelceus, but 

 less so than is usually the case in U. arctos, and the attenuation may be said to com- 

 mence further back. The grinding-surface in the unworn tooth is also much less com- 

 pressed from side to side than it is in U. arctos, though more so than in U. speloBUS. Of 

 the three outer cusps, the anterior two are more nearly of equal size than they are in 

 U. spelceus, and there is no appearance of an accessory intermediate tubercle on the 

 hinder of the two ; the third or posterior cusp is sometimes entirely wanting, and always 

 of insignificant size, and soon worn away. 



In U. arctos the crown in the perfectly unworn or germ condition is much more com- 

 pressed, the two sides falling in, as it were, so as to leave merely a wide furrow between 

 them. There are only two cusps on the outer border, of which the anterior is con- 

 siderably the larger, and the hinder in most cases has a small portion in front con- 

 stricted off so as to form a small accessory tubercle intermediate between the two cusps ; 

 and in this species the internal basal cingulum would appear to be usually less 

 developed than in the others. 



The third lower molar (m. 3) in JI. spelceusis in most cases readily distinguishable by 

 its peculiar form, wliich is also, from what I have observed, tolerably constant. The 

 form of the tooth corresponds, in fact, as might be expected, with that of the expanded 

 upper molar to which it is opposed. The form of the tooth may be described as oblong 

 or subquadrangular, usually with an angle posteriorly. The outer border is divided into 

 two distinct though low cusps by a deep sulcus a little behind the middle of its length. 

 The grinding-surface is very minutely and richly tuberculated or, as it may be said, 

 granulated. The anterior and internal cusp is comparatively little developed. 



In U.fossilis the much smaller tooth is usually of a sub triangular form and generally 

 rounded behind. Sometimes it is more elongated ; but even then it is readily distin- 

 guishable from that of U. spelmus by its greater attenuation posteriorly (corresponding 

 with the upper molar) and other characters. In the typical triangular form there is 

 no sulcus on the outer border, or but a very faint one close to the hinder end ; and this 

 is soon destroyed, if it ever existed, by slight wear. When the tooth is more elongated 

 the outer side presents a shallow sinus, subdividing the border, as in U. spelmis, into 

 two unequal low cusps. The anterior and inner angle of the tooth is raised into a 

 strong conical cusp. The grinding-surface is coarsely plicated or ridged, and rarely 

 tuberculated or granulated in the interstices of the ridges ^. 



' In the figure of the mandibular dentition of U. priscus, in Erit. Fo3s. Mamm. (fig. 35 B) the m. 3 



