454 



the great procoptodont Kangaroos, the vacuity, moreover, extending more forward than 

 in Ildlmaturus or Petrogale. 



I need scarcely say that the dentition of the small existing species of these genera is 

 of the ordinary halrnatural type ; the premolar is trenchant, the inner ridge being low 

 or ' basalt' 



The front pier of the zygoma (Plate XC. figs. 2-5, w, 21"), extending from the 

 fore part of the orbit obliquely downward and backward, terminates below, in the pre- 

 sent immature specimen of Procoptodon, above the interval between d 4 andm 1 ; it might 

 recede in relative position to the molar series when this was fully in place ; but so much 

 of the pier as is preserved is more compressed, and stands out relatively further than in 

 any existing Kangaroo. I shall subsequently be able to show that the more advanced 

 position of the descending masseteric process is constant at all ages in Procoptodon, and 

 may be added to the palatal and dental characters of the genus. 



§ 22. Procoptodon Pusio. — These characters, as above denned, added to size, exem- 

 plify the present species. 



The antero-posterior extent of the three molars d *, mi, m 2, in the subject of 

 figures 2, 3, 6, Plate XC, is 1 inch 10 lines ; the four teeth, the premolar being in 

 place, would reach along 2 inches 4 lines : taking the fore-and-aft diameter of the last 

 molar, m 3, to equal that of the penultimate one, m 1, here in place, the permanent 

 upper molar series of Procoptodon Pusio (ib. fig. 7) would be 3 inches 2 lines in 

 longitudinal extent. All things being equal this Kangaroo was one third larger than 

 Ospkranter robustus, Gd.* 



The subject of figs. 7-10, Plate LXXXIX. is a portion of the right ramus with the 

 three hindmost molars, corresponding in fore-and-aft extent with those of Macropus 

 Titan, but with the following well-marked distinctions. The prebasal ridge does not 

 extend so far forward, and the hind surface has two vertical narrow grooves to which a 

 third shorter and feebler one is added in m 3 (ib. fig. 10, g). These grooves do not 

 extend lower than the valley indicating the base line of the transverse lobes, below which 

 level the common base of those lobes rises smoothly and convexly for a line and a half 

 clear of the socket ; the innermost notch is very little deeper or wider than the next, 

 contrasting with that on the inner half of the hind surface of the molars in Macropus 

 Titan, which descends nearer to the origin of the hind fang of the tooth. Again, the 

 mid link (ib. fig. 9, r) sends off from the inner side near its termination in the hind lobe 

 a short and low ridge of enamel descending to be lost in the inner division of the 

 transverse valley. There is likewise a small vertical ridge from the fore part of the 

 hind lobe internal to the link and its accessory process, which ridge descends straight 

 to the bottom of the valley. These productions of enamel cause corresponding com- 

 plexities of the grinding-surface, which are correlatively associated with a more massive 

 character of bone wielding the grinding instruments. Comparison of fig. 9 with figs. 

 1, 3 of Plate LXXXIX. will exemplify the character of greater thickness, as that of 

 * Compare figure 7, Plate XC. with figure 3, Plate LXXXI. 



