vni ANOMODONTIA 309 



choanae. The occipital condyle is kidney-shaped. The mandible 

 is most extraordinary, approaching that of the Mammalian, 

 especially the Marsupial type, except that it is still composed 

 of several pieces. The articular facet for the mandible is borne 

 by an outward or lateral projection, while the bulk of the 

 posterior half of the jaw projects inwards like a broad flange, 

 undoubtedly recalling the so-called inner inverted angle of the 

 Marsupial jaw. The coronoid process is large and extends 

 far into the temporal fossa. Nearly the whole skeleton of 

 Microgomphodon is known ; the lumbar ribs are broadened and 

 overlap as in CynognatJius, and the mandible is typically 

 compound, so that there is no doubt about the affinities of this 

 genus with the Theriodontia. It throws light upon Gompho- 

 gnathus and the three likewise South African genera Diademodon, 

 Trirachiodon and Tritylodon, which are all known from imperfect 

 skulls only. Their teeth are restricted to the jaws, the molars 

 have flat, multitubercular crowns and bear an extraordinary 

 resemblance to those of Mammals. Some of the molars of 

 Tritylodon are said even to possess two roots, but this point, 

 absolutely unique in Eeptiles, but common in Mammals, is not 

 certain. The few upper incisors of Tritylodon are rather large, 

 chisel -shaped, and extend like those of the Rodent -type back 

 into the maxillaries ; canines are absent, leaving a diastema. 

 Trirachiodon has prominent canines, the five upper molars are 

 multitubercular, rather flat, and much broader transversely than 

 in the longitudinal direction. Still, even these creatures, with 

 skulls of the size of that of a small fox, possessed distinct pre- 

 frontal and postfrontal bones, and are, at least in this respect, 

 typical Eeptiles. 



Order III. ANOMODONTIA. 



The cranium is not roofed in. The pedicle for the suspension 

 of the lower jaw is much elongated, slants slightly forwards, and is 

 composed of the long quadrate, which is laterally overgrown by 

 the squamosal bone. The teeth are restricted to a pair of strong, 

 tusk -like canines, or they are altogether absent. The margins 

 of the upper and especially those of the lower jaw are trenchant, 

 and were possibly furnished with a thick horny armature like 

 those of tortoises. 



