456 



the strongly and broadly inflected angle (ib. a). The lower concavity is bounded below 

 by a feebler inflection of the obtuse lower border of the ramus (ib. d) which soon 

 subsides. This inflected border answers to the more forwardly placed part of that border 

 in Nototherium (Plate XL. fig. 4, d', Not. Mitchelli, Plate XLI. fig. 2,d', Not. Victoria). 

 The correspondence of Procoptodon with Nototherium in this particular, as in the masive 

 proportions of the mandible, is suggestive*. 



The outer surface of the horizontal ramus rapidly gains in vertical convexity as it 

 recedes from the symphysis, but rather loses in vertical extent. The fore border of the 

 coronoid (Plate XCI. fig. 2, q) is thick and obtuse, and rises abruptly and vertically, as 

 in Nototherium (Plate XLI. fig. 1), in advance of the hind end of the molar series ; in 

 the present aged Procoptodon its fore border is on the transverse line of the middle of 

 the last molar (fig. 3, q, m ■*). The channel (fig. 1, u) between the coronoid process (q) 

 and the last molar and postalveolar production is wide and deep. The hind surface of 

 m 3 (fig. 6) is divided into three parts by a pair of feeble vertical indents, the intervening 

 part being impressed by shorter and finer grooves ; there is no postbasal ridge. The 

 mid link receives two small buttress-like ridges on its inner side ; the fore link shows a 

 small swelling or accessory ridge on the same side. The prebasal ridge is as in the 

 subject of fig. 9, Plate LXXX1X. The dentine is exposed on both lobes of the hind- 

 most molar (m 3, Plate XCI.) ; in greater proportion on those of m 2. In the second 

 mandibular fossil (fig. 5) is shown the more worn d 4, and the less worn, later developed, 

 p 3. In the larger specimen (fig. 1) the two fangs only of pa are preserved. They 

 indicate a similar fore-and-aft diameter of this tooth, viz. lines. The extent of the 

 series of five teeth is 2 inches 11 lines, corresponding, as is the case with each individual 

 tooth, in their dimension with their homotypes in the upper jaw (Plate XC. fig. 7). 

 The lower molars differ from the upper ones, as usual, in their minor breadth ; in the 

 hinder surface being impressed at its upper half by numerous fine vertical ridges or 

 wrinkles, and not being excavated ; in the inner part of the fore side of the hind lobe 

 being the seat of longitudinal accessory ridges, instead of the outer half ; in the acces- 

 sory parts of the mid link being produced from the inner, not the outer, side ; in the 

 absence of the backwardly produced borders of the upper half of the hind surface of 

 the front lobe, which, as in the hind lobe of the upper molar, bound or make the exca- 

 vation on that surface ; whereas, in the lower molar, the mid link passes from near the 

 outer end of the flat hind surface of the fore lobe backward. The prebasal ridge with 

 its fore link is more produced in the lower than in the upper molars; the link in the 

 former is supported or thickened by an enamel buttress on its inner side, and the surface 

 of the fore part of the front lobe on the inner side of the link is produced into a pair 

 of low narrow vertical ridges. 



The hind surface of the premolar, at the base of the crown, slopes backward to a 

 medial vertical ridge ; the sides of the crown are compressed and slightly excavated in 

 * Of such facile conjectures, e.g., as that one had been developed into or degenerated from the other. 



