THE SOUTHERN BOTTLENOSED WHALE 



23 



the maxillary crests. These in H. rostratus originate anteriorly approximately equidistantly between 

 rostrum tip and antorbital notch, and ascend in a slope which varies according to age to a summit 

 which overtops the skull vertex in all but the most juvenile specimens. Posterior to the summit 

 there is a decline in level which is generally more abrupt than the anterior slope, the maxillar}' bone 

 attaining normal thickness again before it ascends posteriorly in contact with the vertical portion of 

 the frontal. The crests in H. planifrons originate anteriorly about two-thirds from the anterior end of 

 the distance between rostral tip and antorbital notch. The slope is gradual to a low summit above the 

 antorbital notch, and the decline posteriorly is equally gradual so that there is no horizontal thin 

 portion of maxillary before it rises vertically in contact with the frontal in the occipital crest. In the 

 Discovery specimen the maxillary crests are less massive than in the South Australian specimen. 

 It may be that the difference is associated with sex, but it may equally v/ell be due to difference in age. 



Fig. I. Lateral view of skull and lower jaw. ( x \.) 



The second feature referred to by Flower, and visible in the lateral view of the skull, is the much 

 larger size in H. planifrons of the crest formed by the vertex behind the nares. Not only is it much 

 larger than in H. rostratus but it differs somewhat in shape, overhanging the narial area considerably, 

 whereas in H. rostratus the anterior face of the crest viewed in profile is approximately vertical. Other 

 differences will be mentioned when describing the dorsal aspect. 



In skulls of comparable size the distal portion of the rostrum is more slender in H. rostratus than 

 in H. planifrons. The differences which exist in the proximal portion are associated with the dis- 

 similarity of the maxillary crests. The distance of the maxillary tip from the tip of the premaxilla is 

 alike in both species. 



The extent to which the lachrymal is seen in the lateral view appears to be equally variable in both 

 species. The type specimen of H. planifrons has the left lachrymal completely separating the malar 

 anteriorly from the orbital process of the frontal posteriorly and it has a wide contact with the maxilla. 

 In the Discovery specimen it hardly appears in lateral view. It does not nearly reach the maxilla, and 



