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



In the species about to be described, which I propose to call Dicynodon tigriceps 

 or the Tiger-headed Dicynodon, the general resemblance of the great mammalian 

 Carnivora in the features which most impress the destructive physiognomy upon 

 the skull is sufficiently striking. 



The chief difference, irrespective of size, which the Dicynodon tigriceps presents, 

 as compared with the Dicynodon lacerticeps, is the great expanse of the temporal 

 fossae (PI. XXIX. -, 12, 27, 28), and the great extent of osseous surface for the origins 

 of the temporal muscles, which must have much exceeded the relative size of those 

 muscles in any known existing reptile, and have equalled those of the tiger, lion, 

 and other carnivorous mammals with large canine teeth. 



Like the smaller species of Dicynodon, the D. tigriceps resembled the Iguana, 

 Varani, and many other existing Lizards, in having but one zygomatic arch (Pis. 

 XXIX., XXX. 26, 27, 28), the superadded one, formed by the extension of the post- 

 frontal to the mastoid in the Rynchocephalus* , and in the Crocodiles, not being 

 developed. The normal zygoma formed by the malar (26) and squamosal (27), and 

 by the junction of the latter with the mastoid (s) and tympanic (23), presents in the 

 D. tigriceps, however, a form and expanse quite unique in the class of Reptiles. 



The malar portion (26) quits the lower and hinder angle of the orbit (0), and, as 

 it extends, changes its vertical for an horizontal plane, being, as it were, twisted 

 upon itself so as to turn the upper border outwards : it then coalesces with the 

 squamosal (2?), and the arch is continued backwards, as a broad horizontally dis- 

 posed plate of bone, shghtly convex upwards, to the upper end of the tympanic 

 (28), and the mastoid (s). 



The mastoid (PI. XXXI. «) is continued from the back part of the zygoma (27), 

 bending at almost a right angle as it ascends and passes forwards before con- 

 tracting to join the extremity of the forked parietal (7). Below the mastoid the 

 outer part of the occipital plate (4, paroccipital ?) adds to the bony wall of the 

 temporal fossa, and forms a broad, slightly convex prominence at the back part 

 of that fossa. The inner side of the fossa, which forms a very small portion of the 

 whole, encroaches upon the side of the body of the parietal (7), and is bounded above 

 by a curved ridge of bone (PI. XXIX.) ; the interspace of these parietal ridges is 

 two inches at its narrowest part, which is just behind the median prominence sup- 

 porting the foramen parietale (7), The temporal fossa communicates freely with 

 the orbit (0). 



The breadth of the skull across the broadest part of the zygomata is 18 inches, 

 the length of the skull not exceeding 20 inches ; for the extent of the upper jaw 

 (PI. XXX. 22) in advance of the nostrils may be pretty accurately estimated by the 

 curvature of the portion which is preserved. The extreme breadth of the occipital 



* See PI. VI. figs. 5 & 7. 



