THE SOUTHERN BOTTLENOSED WHALE 



25 



Flower drew attention to the large size of the premaxillar}^' foramina in H. rostratus as compared 

 with H. plaiiifrom, and this is consistent in all the specimens so far described and figured. 



The maxillar)' crests of H. rostratus rise vertically from the external margins of the maxillary 

 foramina, and the inner faces are nearly parallel to one another. In old males especially, the crests 

 approximate to such an extent as nearly to touch and thus form an arch over the prenarial portion 

 of the premaxillae. The medial margins of the maxillary crests of H. planifrons overhang gutter-like 

 extensions forward of the maxillary foramina. The inner faces diverge from each other at a very wide 

 angle, and this feature, together with the lesser height of the crests in H. planifrons, provides one of 

 the most conspicuous diagnostic differences between the two species. 



The vomer, which is without mesorostral ossification, is visible between the overarching anterior 

 portions of the premaxillae. Its anterior tip is nearer the end of the snout in the Discovery specimen 

 than in the South Australian specimen, the distance being 257 mm. as compared with 380 mm. In 

 H. planifrons the greatest width of the premaxillae anterior to the foramina is about midway between 

 the foramina and the premaxilla tip. In H. rostratus the greatest width is at about two-thirds of the 

 distance from the tip. 



VENTRAL VIEW OF SKULL (Fig. 3) 



In ventral view such difl^erences as exist between the skull 

 of H. rostratus and H. planifrons are of detail rather than of 

 fundamental structure. 



The vomer in both species appears as two lenticular areas 

 in the middle line of the rostrum. The anterior area separates 

 the premaxillaries posteriorly and the maxillae anteriorly. 

 There is then a short length where the maxillae are in contact 

 in the middle line before the vomer appears again, when it 

 is bounded partly by maxillae and partly by the palatine and 

 pterygoid bones. 



The anterior portion of the vomer appears to be consistently 

 shorter in H. rostratus than in H. planifrons. 



The palatine bones in both species are in two portions, 

 palatal and lateral, separated by the pterygoid coming into 

 contact with the maxilla. The palatal portion is bounded by 

 maxilla, vomer and pterygoid, the lateral part by pterygoid 

 and maxilla. In H. planifrons the palatal portion is a narrow 

 strip with a greatest width, in the Discovery specimen, of 

 less than a centimetre, and a length of about 10 cm. Each 

 palatal portion in H. rostratus is roughly triangular in outline 

 and of greater expanse (width about 4 cm. and length 11-5 cm., 

 in a specimen of size comparable to H. planifrons). This 

 diff'erence appears to be constant. The space between the 

 palatal and lateral portion of the palatine, where the pterygoid 

 anteriorly comes in contact with the maxilla, is much greater 

 in H. planifrons than, in proportion to skull length, in any 

 of the H. rostratus skulls in the British Museum collection. 

 Incidentally it may be remarked that in Berardius arnuxii 

 the palatal and lateral portions come into contact, being 



Fig. 3. Ventral view of skull. 



( X l) 



