238 Prof. Owen on the Reptilian Fossils of South Africa. 



The trenchant edentulous border rises as it advances from the tusk-socket, and 

 then shghtly descends to the fore part of the beak-hke termination of the upper jaw. 



Lower jaw. — Of this there is the anterior portion, including the symphysis, 

 where the rami are extensively confluent ; such portion being conformable 

 in size with the above-described cranium of the Dicynodon tigriceps. The 

 symphysis (PI. XXX. 32) is deep, curved lengthwise, with the convexity for- 

 wards, and more convex transversely ; it appears to have been traversed by a 

 median low obtuse ridge externally, corresponding to the median ridge of the 

 premaxillary : its extent following the curve is not less than seven inches ; its 

 breadth, following the curve, three and a half inches. An extent of seven inches 

 of the alveolar border of the left ramus is preserved ; this border shows a slightly 

 convex, prominent, vertical, longitudinal ridge on its inner side, a straight and 

 lower ridge on its outer side, and an intervening groove, which, beginning five 

 inches from the fore part of the jaw, gradually acquires a depth of six lines at the 

 fractured end of the ramus. Not the slightest trace of teeth is visible. A strong 

 longitudinal obtuse angular bar of bone (a?) begins to project from the outside of 

 the ramus, four inches from the anterior end of the jaw, and one inch below the 

 alveolar border. The dentary element shows a notch [v) below the back part of 

 the bar indicative of a small vacuity in this part of the jaw. The fractured 

 surfaces of the rami expose the vertical fissure or division of the dentary element 

 for junction with the hinder elements of the compound bone. 



In the shape and extent of the symphysis, and in the exterior bar or ridge, the 

 lower jaw of the present large species repeats the generic modifications, pre- 

 viously described, of that of the smaller species of Dicynodon. 



Comparison of the Dicynodon tigriceps with the D. lacerticeps. 



The most complete of the smaller skulls described in the first part of this Report* 

 had been mutilated to the same extent by the breaking off of the upper jaw anterior 

 to the nostrils, as is the best preserved of the larger skulls here described ; but 

 being similarly perfect in other respects, it affords the subject of an instructive 

 comparison. 



On a side view, the Dicynodon tigriceps differs from the D. lacerticeps in the 

 relatively larger size of the temporal fossa and in the smaller size of the orbit : the 

 great expanse of the temporal fossa involves also a different relative position of the 

 orbit, which in D. lacerticeps occupies the middle third of the skull ; whilst in D. 

 tigriceps it is in the anterior half: the orbit is also of a different form, being almost 

 circular in D. lacerticeps, and equalling the temporal fossa in size. The nostrils 

 also appear to be relatively larger in D. lacerticeps, but this difference may be 



* See above, p. 62, and PI. iii. 



