98 
FOSSIL JAWS OF MACROPODID^, 
exteriorly, increasing in depth posteriorly. Lower contour line 
straight or arched upwards. Incisor proclivous, spatulate. 
Symphysis lax. 
Dimensions. 
Mandibular. — The full series of cheek-teeth is from 55'8 to 
58-6 in length (2); the first three molars 30-1 to 31-6 (2); the 
premolar 12-1 x 6-8 to 12-8 x 7 (2). The width of m. 3 is from 
8-9 to 10-5. The anterior depth is from 26-1 to 28'5 (4); the 
posterior from 29-0 to 32-7 (4); the thickness from 14-8 to 15-6 
(4). 
Form. 
Mandibular. — P. 3 (PL xvi. fig. 9). This tooth as exemplified 
by the anterior two-thirds of its crown in a mandibular fragment 
is structurally similar to its successor p. 4 , but the extero-posterior 
complicated region of the crown is not evidently marked off by an 
oblique cleft. On the outer surface of this region there is a 
distinct trace of an outstanding cusp corresponding to that in p. 4 
of S. pales. 
Molars. — Mr. Lydekker's statement that in Sthenurus there are 
no " vertical folds " must be understood to refer only to the lateral 
processes of the longitudinal links, as the latter exist in 8. goliah 
and S. otuel. Of the presence in the type of the genus of tapering 
folds lying upon the anterior surface of the lobes as we have seen 
them in all the species now referred to it there is no doubt; there 
is indeed evidence of the fact in the figure of m. 3 in II. PL 82, fig. 
9, though no mention of it is made by Owen. In the mutilated 
tooth now figured (PL xvi. fig. 11) from a mandible having the 
characteristic premolar rising into place the incumbent folds are 
well marked fully in the hind lobe and by their bases in the 
broken fore lobe." 55 " 
* Complication of structure is more frequently found in the anterior 
molars than in the posterior; nay, even the fore lobe of the last molar 
rather than in the hind. It is therefore unsafe to pronounce teeth free 
from folds unless the young jaw is found without them, or to neglect the 
slightest trace of such folds which may remain in worn teeth. 
