PROF. W. H. FLOWER 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 /. australis, and that it departs, therefore, in this 
character, still further from (the young) MW. grayi. 
The cranium of MW. 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 basisphenoidal 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 I. bidens and, in fact, of all 
others of the genus, is that the upper extremities of the premaxille 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 premaxille, 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 MW. australis, and therefore equal 
to that of MW. 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 IZ. bidens. As the tympanic bone of Berardius is 
constructed on exactly the same type as that of Mesoplodon, this bone gives no assist- 
ance in determining the supposed relationship of MW. hectori to Berardius. 
VOL. x.—PART 1X. No, 3.—August 1st, 1878. 3M 
