453 



ransversely ridged complexity of the broad working-surface between the outer (a) and 

 inner (b) longitudinal ridges or walls (fig. 7), which shows it to have acted as a pounder 

 rather than a divider of the vegetable food, a character which suggested the name pro- 

 posed for the genus (Note *, p. 451). 



The vertical extent of the enamelled crown of the premolar does not exceed the 

 breadth of the hind part of the tooth. The outer surface shows three conical elevations, 

 in low relief, of the enamel, one behind another (fig. 2, p 3). The apex of the foremost 

 constitutes the anterior prominence of the outer longitudinal ridge ; that of the second 

 slightly projects from the middle of that ridge (a, p s, fig. 7) ; that of the hindmost one 

 subsides before it gains the ridge, which is continued, sharply, upon the outer and back 

 part of the crown of the premolar. The foremost of the three conical low reliefs of the 

 enamel forms the outer part of the fore swollen end of the crown (fig. 4,^)3), which is 

 divided by a depression from the lower and narrower, basally swollen beginning of the 

 inner longitudinal ridge (b). This slightly diverges as it recedes from the outer ridge, 

 obeying the hinder enlargement of the crown, and it is united near that end by a trans- 

 verse ridge with the outer longitudinal one. The transverse ridge is a miniature or 

 rudiment of a hind lobe, and its hind surface is excavated and ridged in a feeble or 

 rudimental way like that part of the normal hind lobe of the bilophodont molars. The 

 horizontal triturating surface of the premolar between the outer and inner longitudinal 

 ridges is sculptured by transverse sharp enamel-ridges and deep depressions. 



There is a character in the upper jaw of Procoptodon which is not present in the 

 large existing Kangaroos of the subgenera Macropus and Osphranter. It is present, 

 under some modifications, in Boriogale and in the smaller Kangaroos or Wallabies 

 of the subgenera Halmaturus and Petrogale. I find, indeed, in Petrogale xan- 

 thopus, Gd., and Halmaturus brachyurus, Wth. (Plate XC. fig. 1, b b), the nearest 

 approach to the structure in question. It is a large unossified tract of the palate, shown 

 in both maxillaries of the fossil (ib. fig. 6, b b) by the passage of the palatine (fig. 3, 21) 

 into the nasal (n) plate at a distance of from 2\ lines to 3 lines from the inner wall of 

 the alveoli of d *, m 1, and m 2. This upward bend of the palatal plate (ib. fig. 3, n) is 

 at nearly a right angle with the narrow horizontal palatal strip, and in both maxillae the 

 continuation of the nasal plate of the maxillary into the orbital one by the large spheno- 

 palatine foramen (fig. 3, s) is shown. 



Arrested ossification of the palate is, however, a marsupial rather than a macropodal 

 character, and is exemplified, in my " Osteology of the Marsupialia"*, in the Thylacine, 

 the Sarcophile, the Dasyure, the Bandicoots, the Peragale, and the Potoroo, as well as in 

 a small species of Kangaroo [Halmaturus Bennettii). In this species the palatal vacuities 

 are four in number, in two lateral pairs f. In Halmaturus brachyurus (Plate XC. 

 fig. 1, b b) the intervening strip of bone between the fore and hind vacuity is wanting, 

 and each pair is blended into one large lateral unossified tract, which either falls into its 

 fellow, or is separated from it by a mere filament of bone. Such was the structure in 



* Zoological Transactions, 4to, vol. ii. part 1, 1838, p. 388, plates 70 & 71. t Op. cit. pi. 71. fig. 5. 



47* 



