418 PROF. W. H. FLOWER ON THE GENUS MESOPLODON, 
mandible, as in VW. hectori, or near the hinder part of the symphysis, as in all the 
others, forms another good distinctive character. 
e. Finally, the character and form of this tooth presents some important variations. 
In W. layardi, its apex is everted, and seated upon a flat strap-like base, which grows 
upwards, backwards, and finally inwards, closing over the upper jaw and meeting its 
fellow of the opposite side. In MW. densirostris the apex is directed vertically, placed 
on a very massive base, which is implanted in a greatly expanded alveolar margin of 
the jaw, not found in any of the other species. In M. grayi the tooth is triangular 
and compressed, and the apex is vertical at all ages. In MV. hectori the apex of the 
tooth in the young animal is directed forwards. In JM. bidens the apex of the tooth is 
at first directed backwards, but during growth becomes rotated forwards. In the only 
specimen of M. ewropeus known (an adult) the apex of the tooth is directed somewhat 
forwards. 
These characters may be thus placed in a synoptical form :— 











Lateral Premaxillary a 
basirostral foramen to Position of Other dental characters. 
groove. maxillary. mandibular tooth. 
Absent. Level. Closontovapexmola || fc eerie. tries oie | M. hectori. 
mandible. 
Absent. Level. Aad etOL Mara enlace ee eteteleteretene aesere | MW. europeus. 
dibular sym- 
physis. 
Absent. Level. Near hinder edge | Apex of tooth at first di- | MW. bidens. 
of mandibular rected backwards, and 
symphysis. during growth rotated 
forwards. 
Shght. Level. Ditto. Apex of tooth everted and | M. layardi. 
mounted on a flattened 
base, which increases in a 
length with age, and 
finally curves round the 
maxilla. 
Deep. Behind. Ditto. Apex of tooth vertical. Al- | WM. densirostris. 
veolar portion of jaw 
expanded. 
Deep. Behind. Ditto. Apex of tooth vertical. A | If. grayi. 
row of small teeth in 
upper jaw. 


Besides the above, there are many minor differences, more appreciable by a com- 
parison of the specimens than by description, some of which will be pointed out in 
the sequel. 
The special materials upon which the present confmunication is based are :— 
1. The skull of a young specimen of W. hectori, the type and at present only known 
It was taken in Titai Bay, Cook’s Strait, January 1866 ; and 
the skull is figured by Dr. Hector in the Trans. New-Zeal. Inst. vol. iii. 1870, pls. xiv. 
example of that species. 

