428 PROF, W. H. FLOWER ON THE GENUS MESOPLODON. 
species’. The tooth is in a very early stage of development, being merely a hollow 
cap of dentine, with a smooth and enamelled tip, and entirely embedded within the 
alveolus. The formation of the base of osteo-dentine appears not to have com- 
menced. It is compressed and triangular, smaller than the young specimen of MW. grayt 
described above, and of different form, being narrower at the base, compared with the 
height; but, as in that specimen, the apex was placed quite vertically. From so very 
young a tooth it is not safe to draw conclusions as to the ultimate form the organ 
would assume. 
With regard to MW. hectori the same difficulty exists. The only specimen known is 
so young as to have the teeth entirely embedded in the alveoli; but, as before men- 
tioned, their situation at the anterior extremity of the mandible distinguishes this 
from all other species. The apex, which is the anterior part of the tooth as it lies in 
its socket, is exactly 1 inch from the anterior margin of the symphysis. The tooth is 
very much compressed, being no where more than 5 millims. in breadth, The base is 
composed of two lamin, nearly in contact, with an open fissure between them. The 
point is sharp, capped with enamel to the extent of 8 millims. The height of the 
tooth is 1""2 or 31 millims., the antero-posterior diameter of base 11 or 28 millims. 
Vertebral Column.—The length of the vertebral column of the adult MW. australis, all 
the bones being placed in apposition, is 150 inches. Allowing the same increase for 
the intervertebral substance which was found in a common Porpoise, viz. as 115 is to 
100°, we should obtain a length of 150 inches; the length of the skull (30 inches) 
added to this gives a total length of 180 inches, or 15 feet, for the whole skeleton, 
which corresponds very closely with Dr. Hector’s measurement of 15 feet 6 inches for 
the animal when recent ®. 
In the younger skeleton of the typical 1/7. grayi the vertebrae measure 125 inches; 
and by the same process the whole skeleton would be 14 feet 3 inches, rather more 
than the length given by Dr. Haast, viz. 13 feet 8 inches; but of course the allowance 
made above for the intervertebral substance is only approximative. Dr. Haast gives 
the length of an adult female of the same species as 17 feet 6 inches+. 
The skeleton of MW. australis has the following vertebral formula:—C. 7, D. 9, L. 11, 
C. 20 = 47; that of IZ grayi has C. 7, D. 10, L. 11, C. 20 = 48. In both cases there 
is probably one minute terminal vertebra wanting. 
These numbers closely correspond to those of the few other complete skeletons of 
Mesoplodon known, viz.:—that of I. bidens at Brussels, which has (according to Van 
Beneden) C. 7, D.10, L. 10, C.19 = 46; that of the same species at Gothenburg, 
which has C.7, D. 10, L. 9, C. 20 = 46 (Malm); and that of I. layardi, at the Canter- 
' Notice of a variation in the dentition of Mesoplodon hectori, Gray, Trans. N.Z. I. vol. vi. p. 86, pl. xv. a, 
1874. 
2 See Trans. Zool. Soe. vol. vi. p. 311. ° Trans. New-Zeal. Inst. vol. vii. p. 262. 
* Proc. Zool. Soc, 1876, p. 457. 
