PEOF. W. H. FLO WEE ON THE GENUS MESOPLODON. 423 



of growth to that in fig. 3. If so, most of the determinations of the fossil species based 

 solely upon the form of the rostrum are quite valueless. 



It should be mentioned that in this fragmentary rostrum the lateral groove and pit 

 at its base are deeper even than in M. australis, and that it departs, therefore, in this 

 character, still further from (the young) M. grayi. 



The cranium of M. hectori, from Titai Bay, New Zealand, now in the British 

 Museum, presents a conformation quite distinct from that of either of the specimens 

 last under consideration. As is shown in the synoptical table at p. 418, it more nearly 

 resembles the northern species in the relation of the maxillary foramina, the absence of 

 the basirostral groove, and, it may be added, the correlated greater breadth of the base 

 of the rostrum. The skull is evidently that of a very young animal : the teeth are still 

 concealed beneath the gum; the symphysis of the lower jaw is not united; the meso- 

 rostral cartilage is entirely unossified ; the basi sphenoidal suture is open (as seen 

 from the interior of the cranium ; for on the outer surface it is covered by the vomer) ; 

 and the bones generally are very spongy and greasy. On the other hand, the elements 

 of the occipital bone have all coalesced with each other and with the basisphenoid. 

 The principal difference between this cranium and that of M. Mdens and, in fact, of all 

 others of the genus, is that the upper extremities of the prsemaxillse are less developed 

 laterally and less everted, and therefore approximate more to the form of Berardius ; 

 but unfortunately a large piece of one of these bones is broken off from the right side, 

 or that which is usually most strongly marked, and it is impossible to say how much of 

 the absence of characteristic eversion may be due to the immaturity of the specimen. 

 There is also a greater elevation of the longitudinal ridge on the upper surface of the 

 maxilla, immediately to the inner side of the anteorbital notch, than in any other 

 Mesoplodon. This ridge, it should be remarked, forms a strongly pronounced elevation 

 in Berardius, and is developed in Hyperoodon into the immense bony mass which forms 

 such a characteristic feature of the skull of that genus. The nasals, however, are com- 

 pletely sunk between the ends of the prsemaxilke, whereas in Berardius they form 

 prominent masses rising to the vertex. 



The palate-bones only appear on the palatal surface as narrow strips on the outside 

 of the pterygoids, not reaching as far forwards as they do. The vomer is visible in 

 the middle third of the inferior surface of the rostrum. 



The mastoids and squamosals are quite free ; and the former are largely developed, 

 forming the principal part of the great post-tympanic processes of the skull. 



The tympanic is very slightly larger than that of M. australis, and therefore equal 

 to that of M. grayi, and presents a very close resemblance to both, but is nearer in the 

 form of the lobes at the posterior part to the former. I have not had an opportunity 

 of comparing it with the tympanic of M. Mdens. As the tympanic bone of Berardius is 

 constructed on exactly the same type as that of Mesoplodon, this bone gives no 

 ance in determining the supposed relationship of M. hectori to Berardius, 



vol. x.— part ix. No. 3. — August 1st, 1878. 3 m 



