24 



DISCOVERY REPORTS 



the malar and frontal are in contact above it. The H. rostraius specimens examined showed a variety 

 of form in the lachrymal. In one it did not appear in lateral view, in another there was a ventral 

 portion separated from a more dorsal portion by a considerable extent where malar and frontal were 

 in contact, and in a third the lachrymal completely separated malar from frontal and was in contact 

 dorsally with the maxilla. This variation in the H. rostratus lachrymal is apparently connected neither 

 with the age nor the sex of the animal. 



The temporal fossa in the Discovery specimen, like that of the type, is higher and shorter antero- 

 posteriorly than that of H. rostratus. Apart from these differences the general form of the skulls is 

 very similar and confirms the generic affinity of the two species with each other. 



DORSAL VIEW OF SKULL (Fig. 2) 

 The differences between H. rostratus and H. planifrom are again clearly seen in the dorsal view. The 

 massive prominences over the nares in H. planifrons 

 extend forward so that the anterior boundary of the right 

 one is almost vertically above the premaxillary foramen. 

 The left, smaller in size, does not extend forward quite 

 so far, but both in this aspect shut out any view of the 

 narial apertures. The two bones are separated from each 

 other by a parallel-sided gap bounded by the nasals. Hale 

 states that in the South Australian specimen ' The inner 

 anterior edge of each nasal (at the bottom of the groove) 

 drawn up into a low thin flange'. This is the condition 

 in the type, but in the Discovery specimen the flanges 

 are wanting, so that there is no median ridge at the hinder 

 end of the groove. All the specimens show the internasal 

 gap diverging to the left from behind forwards and con- 

 tributing to the asymmetry which characterizes the whole 

 of this region of the skull. In H. rostratus the narial 

 prominences do not extend forward so as to shut out 

 completely the view of the nares ; the right boss, still larger 

 than the left, has a greater width to length proportion than 

 in H. planifrons. The internarial groove is wider, and has 

 divergent, not parallel, sides. The nasal septum is similar 

 in both species. It is strongly deflected to the left anterior 

 to a pronounced emargination, and overlays to some extent 

 the left premaxillary. Its extension forward in the gutter 

 of the vomer is similar in the Discovery and the type 

 specimen, in both of which it ends in the region of the 

 posterior edge of the maxillary foramina about 100 mm. 

 behind the level of the antorbital notches. The South 

 Australian specimen has this ossification extending forward 

 nearly to the antorbital notch level. 



In the region of the antorbital tubercle the outline of the skull is consistently different in the two 

 species. In H. planifrons from the apex of the tubercle the external outline of the antorbital region 

 extends posteriorly at an obtuse angle with the external edge of orbital process of the frontal, whereas 

 in H. rostratus it is very nearly a right angle. 



Fig. 2. Dorsal view of skull. ( x J.) 



