78 Geological Society : — 



duced and notched in the middle ; the occipital plane, owing to 

 the outward expansion of the mastoid plates, is the broadest 

 part of the skull, which quickly contracts forward to the ridged 

 beginnings of the alveoli of the canine tusks; orbits oblong, 

 reniform, suggestive of the reptile having the power of turning the 

 eyeball, so as to look upward and backward as well as outward. 

 Remains of sclerotic plates. Nostrils divided by a broad, flat, upward 

 production of premaxillary, situated nearer the orbit than the 

 muzzle, smaller than in type Dicynodon ; temporal fossae broader 

 than long, and with the outer border longest ; palate with single 

 large oval vacuity, bounded by palato-pterygoid ridges ; occipital 

 hypapophyses proportionally thicker than in Dicynodon tigriceps ; 

 no trace of median suture in parietal, which is perforated by a * fora- 

 men parietale ;* frontals divided by a median suture and supporting a 

 transverse pair of small tuberosities ; anterior boundary-ridge of 

 vertex formed by the nasals and prefrontals, the outer surface of 

 both being divided into a horizontal and sloping facet ; lacrymal 

 bone extending from fore-part of orbit half an inch upon the face to 

 the nostril ; premaxillary long and single, its median facial tract 

 flat, with a low median longitudinal ridge ; maxillaries forming the 

 lower boundary of the nostrils, and uniting above with the pre- 

 frontal, lacrymal, and nasal bones, their outer surface divided by the 

 strong ridge suggesting the subgeneric name ; teeth of the upper 

 jaw restricted to the two canine tusks, the sockets of which descend 

 much below the edentulous alveolar border ; lower jaw edentulous, 

 deep, and broad, with the fore-part of the symphysis produced and 

 bent up to meet the seemingly truncate end of the premaxillary, — a 

 character indicating, with the angular outline of the skull, the sub- 

 generic distinction. 



Ptychognathus verticalis. — The skull of this species, repeating the 

 subgeneric characteristics of the foregoing, has the facial contour 

 descending almost vertically from, and at almost a right angle with, 

 the fronto- parietal plane. Orbits proportionally larger and more 

 fully oval. Ridged sockets of the canine tusks descending more 

 vertically from below the orbits. Originals transmitted to the 

 British Museum by Governor Sir George Grey, K.C.B., from Rhen- 

 osterberg, South Africa. 



Subgenus Oudenodon, Bain (ovdels, none, ohoi/s, tooth). — The 

 skull in this subgenus presents the divided nostrils, the structure 

 and the rounded contours of that of the true Dicynodons ; also the 

 same form, relative size, and position of the orbits and nostrils ; 

 but the zygomatic arches are more slender, straight, and long ; and, 

 although there be an indication of an alveolar process of the supe- 

 rior maxillary, the lower part of which projects slightly beyond the 

 rest of the edentulous border of the jaw, it does not contain any 

 trace of a tooth, so that both jaws are edentulous, — a character which 

 had attracted the attention of their discoverer, Mr. Bain, who, in 

 indicating it, proposed the name Oudenodon. 



It is permissible to speculate on the possibility of these toothless 

 ynodontoids being, aftsr the analogy of th Narwhals, the 



