280 



The socket of the first molar (d b) begins in this young jaw one inch behind the opening 

 of that of the incisive tooth, which gives the length of the diastema (ib. fig. 1, k) at this 

 stage of dentition. The first molar has an anterior and a posterior lobe. The front lobe 

 is highest, and is a three-sided cone, with one angle in front and rather produced or ridge- 

 like ; it is subcanaliculate internally: the two posterior angles are continued into the 

 fore and hind borders of the hind lobe ; this is transverse, low, flat, inclined from behind 

 forward and rather downward to the base of the front lobe. Both lobes are convex 

 outwardly, and separated there by a shallow depression ; the inner side of the tooth is 

 much lower than the outer one. The fore-and-aft diameter of the crown is 9 lines, the 

 transverse diameter posteriorly 6| lines; it is implanted by two fangs (ib. fig. 5, I), one 

 behind the other, and each 10 lines in length ; the entire length of the tooth, vertically, 

 is 1 inch 6 lines. 



The second molar (ib. d 4) assumes the two transversely ridged or bilophodont type, 

 the lobes being in the form of transverse wedges. The anterior lobe is narrower trans- 

 versely, broader from before backward than the posterior one. The anterior basal ridge 

 ( /') is a continuation of the slightly produced fore margins of the outer and inner sides 

 of the front lobe, at their lower ends, into one another, defining below the slightly exca- 

 vated surface on the fore part of the anterior lobe, the enamel of which is finely rugous. 

 From the junction of the basal with the outer vertical ridge, a similar ridge is continued 

 curving downward and backward, and then rising upon the posterior part of the outer 

 surface of the front lobe (ib. fig. 1, a), defining upon that surface a finely rugous tract of 

 enamel. The inner side of the front lobe (ib. fig. 4, a) has no such ridge. The hind 

 surface of this lobe is less definitely bounded by a backward prominence of the outer 

 border, and a slight vertical ridge or fold of enamel near the inner border. The valley 

 (h) between the lobes has both the outer and inner entry crossed by a short ridge, the 

 outer one being the strongest. The posterior basal ridge (y) is the broadest ; its outer 

 and inner ends bend up a short way upon the hind surface of the hind lobe. The line 

 of initial abrasion at the edges of the two lobes is from above downward and backward. 

 Both lobes present in profile a slight curve backward. The length (fore-and-aft dia- 

 meter) of the tooth is 1 inch 2 lines ; the- breadth (transverse diameter) of the front 

 lobe is 9 lines, that of the hind lobe is 11 lines. It is broader in proportion to its length 

 than in Biprotodon*. The anterior and posterior basal ridges are narrower, relatively, 

 than in that genus. 



The third molar (Plate XL., m 1) has the two lobes of equal breadth save at the sum- 

 mit, where this dimension rather exceeds in the hind lobe : the front lobe rises higher 

 than the hind one. The front basal ridge is continued more abruptly from the anterior 

 angle of the inner border of the lobe than in d 4, and it passes outward to the base of 

 the outer end of that lobe, like a " cingulum," without being continued upward into 

 the outer prominence bounding that part of the front surface of the front lobe (fig. 3, m 1). 

 This surface, as in the second molar, is finely rugous ; it is concave transversely, convex 



* Plate XXIV. figs. 2 & 3, 4. 



