PEOFESSOE OWEN ON THE FOSSIL MAMMALS OF AIJSTEALIA. 



529 



third of the inner surface. The hinder and two-thirds of the inner sides of i 1 arc thus 

 uncoated by enamel, the dentine [d) showing there only a thin coating of cement (c). 



The surface of the enamel is longitudinally striate and punctate (Plate XXXVI. figs. 

 3 & 4) ; the fine pits being chiefly but not wholly between the strise ; so that in some 

 parts the surface seems to be minutely reticulate or reticulo-punctate. The surface of 

 the dentine to which the enamel was applied shows a similar but less marked character. 

 The cement {c) is thickest where it overlaps the terminal edges of the enamel. 



The second upper incisor (Plate XXXV. fig. 1, ^■2 ; Plate XXXIX. fig. 7) is slightly 

 curved, but in an opposite direction to the first, the anterior longitudinal outline being 

 concave : the degree of this bend seems greater through the oblique attrition of the 

 tooth from behind downward and forward. The transverse section of this incisor is 

 subcircular. The length of the exposed part of the tooth is 3 inches ; the circumference 

 is 3 inches 6 lines ; but this slightly diminishes to the margin of the socket, and more 

 so to the inserted end. The fore-and-aft extent of the abraded working-surface of the 

 tooth (ib. fig. 8) is 1 inch 6 lines. The length of the entire tooth does not exceed 4 inches. 



The third upper incisor (Plate XXXV. fig. 1, ^3), of similar form, is smaller. The 

 length of the exposed part is 2 inches 10 lines; its circumference is the same; the fore- 

 and-aft extent of the worn surface is 1 inch. This surface runs upon the same level as. 

 that of the second incisor. The crown of the large lower incisor, besides applying its. 

 trenchant edge against that of the broader front incisor, scraped upon both the smaller 

 incisive teeth. Probably, by reason of the age of the individual and the extent of tooth 

 worn away, the original enamelled crown has gone, and both i 2 and i 3 are here repre- 

 sented only by their cylindrical cement-covered portion. 



A specimen of a detached second upper incisor is in the same condition : the ena- 

 melled crown is worn away, the root contracts to its implanted end, which shows a small 

 remnant of a conical pulp-cavity 8 lines in depth and the same in width, as in fig. 7, 

 Plate XXXIX. 



The second and third incisors of Diprotodo7i w^ere teeth of limited growth, and wdth 

 the enamel confined to and thus defining a crown as in the Kangaroos ; whilst the front 

 incisor was a scalpriform tooth as in the Wombats, in which the second and third inci- 

 sors are not developed. The extinct JDiprotodon thus exemplifies an interesting inter- 

 mediate or transitional condition of the upper " dentes primores " unknown in any existing 

 form of Marsupialia. 



In the upper jaw of the skull above described (Plate XXXV.) the molar series is in 

 place, with the exception of the first small tooth {d 3). The other four teeth occupy, on 

 each side the jaw, a longitudinal alveolar extent of 7 inches 4 lines. The homologies of 

 these teeth with those in Macropus are indicated by the symbols used in my ' Anatomy 

 of Vertebrates,' vol. iii. fig. 296, where the grounds for such use are given, and in fig. 1, 

 Plate XXXV. of the present Memoir. Scarcely a trace of the socket of the first small 

 molar {d 3) remains in the skull ; the other molars progressively increase in size to the 

 last {m 3), which has a minor breadth of the hind lobe than in m 2. The line of the 



4 c 2 



