2l6 PATACONIAN EXPEDITIONS: PALAEONTOLOGY. 



vertical and has a broad median convexity, which dorsally curves forward 

 upon the roof of the cranium for a short distance and much farther in the 

 immature skull ; in the adult this extension is much less and the occipital 

 crest is better developed than in most of the other species of this genus, 

 but in the young animal the crest is very low and indistinct on the sides, 

 and dorsally dies away altogether. Another difference between the young 

 and the adult skull is in the median convexity of the occiput, which 

 lodges the vermis of the cerebellum, and is much more prominent in the 

 former than in the latter ; the paroccipital processes are unusually well- 

 defined. Only a narrow strip of the periotic is exposed upon the surface 

 of the skull and there is no fossa between the exoccipital and squamosal. 



The forehead is broad and nearly flat, the frontal sinuses producing 

 hardly any convexity, and the postorbital processes are very feebly indi- 

 cated. The nasals are short and very wide ; anteriorly they have the 

 same deep lateral notches as in the species previously described, but the 

 median anterior processes are broader and more bluntly pointed. The 

 hard palate is wide and uncommonly flat, being but slightly convex 

 between the molariform teeth, and the vascular perforations are fewer 

 and smaller than in most of the species, but in the fully adult animal the 

 palate has a peculiar granulated appearance ; the notch for the premaxil- 

 lary is a deep, narrow U. The anterior nares are low and wide ; the roof 

 is formed entirely by the nasals, the maxillaries not curving inward dor- 

 sally, as they do in the species with narrow nasals. 



Unfortunately, the mandible is unknown; a knowledge of it might 

 necessitate the union of this species with H. grandis. 



MEASUREMENTS. 



No. 9,176. No. 15,596. 



Skull, length in median line (exclusive of premaxillae) .......... 129 .125 



" " from occipital condyles to anterior nares ........... 150 .152 



" width at postorbital constriction ....................... 036 .039 



" " over lachrymals ............................... 065 .068 



Cranium, length, occipital condyle to rim of orbit ............... 116 .119 



Face, length, orbit to anterior nares .......................... 036 .034 



Occiput, height ........................................... 046 .043 



" width at base ..................................... 062 .067 



Zygomatic arch, length .................................... 084 .08 1 



Length from occipital condyle to glenoid cavity ................ 027 .024 



Rostrum, width at base .................................... 034 .041 



