423 



diphyodont dentition* ; its crown differs from that of the younger (type) Sthenurus Atlas 

 only in a slight superiority of size. The prebasal ridge is linked to near the middle of 

 the front transverse lobe, a little nearer the outer side, making the worn surface there 

 somewhat thicker ; the mid link rising from the middle of the base of the hind part of 

 the front lobe rises to join the hind lobe at a similar position, and with a similar result 

 to the grinding-surface. The more produced prebasal ridge of the next molar presses 

 upon the back part of the hind transverse lobe of d 4, above the feeble outswelling of 

 the base of that tooth. The fore-and-aft extent of the prebasal ridge, with its linking 

 bar inclining obliquely outward to abut upon the front transverse lobe, characterizes 

 the three true molars, m 1, 2, 3. The transverse breadth of the hind lobe of m 3 is rather 

 less than that of the front lobe. 



The molar series of the present mandible describes a feeble convexity outward. 

 The figures in Plate LXXXII. being of the natural size precludes the need of recording 

 admeasurements. 



The subject of figs. 7 & 8, Plate LXXXIV., and of fig. 9, Plate LXXXII., is a portion 

 of the left mandibular ramus (drawn in the Plate without reversing) of Sthenurus Atlas, 

 from an older individual than that which afforded the more entire ramus, but retaining 

 the four first molars and part of the socket of the fifth. 



The outer and posterior lobe of the premolar (Plate LXXXII. fig. 9, jp 3, b) has been 

 worn down below the level of the posterior part of the antero-internal lobe (Plate 

 LXXXIV. figs. 7 & 8, c), which stands up as an angular trenchant ridge ; on the broader 

 outer lobe a flat field of dentine is exposed, showing that the back part of this premolar, 

 as in Nototherium, took some share in mastication, not merely in division of the food 

 as in Halmaturus ualabatus ; so much of the grooves, ridges, and other accentuations 

 of the crown of j> 3 as remain in the present specimen repeat those characters in the 

 unworn homologue of the two preceding specimens. 



The crown of d 4 (Plate LXXXII. fig. 9) shows a field of dentine enclosed by a border 

 of enamel encroaching by a curved indent in opposite sides, and with a feeble fold at the 

 outer part of what was the prebasal ridge. The dentine of this ridge is worn in m 1 

 into continuity with that of the front lobe, and a small portion of the same tissue is 

 exposed on the back lobe. In m 2 the enamelled summits of the transverse lobes are 

 worn obliquely backward, the enamel showing there a finely polished tract. The basal 

 swelling at the back part of this molar is better defined than in the type specimen ; 

 in neither is the hind surface of the molars impressed as in Macropus Titan. The present 

 specimen agrees in size with the comparable or homotypal parts of the upper jaw 

 (Plate LXXXIV. figs. 4, 5, 6). The slight difference of size as compared with the man- 

 dible of the younger individual (Plate LXXXII. figs. 5, 6, 8) is well within the limits 

 of individual and sexual range of variety. 



The outer surface of the portion of mandible of Sthenurus Atlas (Plate LXXXIV. fig. 7) 

 shows a longitudinal sinuous shallow channel, extending from below the fore part of p 3 



* Ante, p. 209, fig. 3 (Sus). 



43* 



