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 M. grayi 

 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 M. 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 laminae, 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 l"'l or 28 millims. 



Vertebral Column. — The length of the vertebral column of the adult M. australis, all 

 the bones being placed in apposition, is 130 inches. Allowing the same increase for 

 the intervertebral substance which was found in a common Porpoise, viz. as 115 is to 

 100 2, 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 M. grayi the vertebrae measure 123 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 oi M. australis has the following vertebral formula: — C. 7, D. 9, L. 11, 

 C. 20 = 47 ; that of M. 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 M. hidens 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 ilf. layardi, at the Canter- 



' Notice of a variation in the dentition of Mesoplodon hecton, Gray, Trans. N.Z. I. vol. vi. p. 86, pi. xv. a, 

 1874. 



■ See Trans. Zool. Soc. vol. vi. p. 311. ' Trans. New-Zeal. Inst. vol. vii. p. 262. 



' Proc. Zool. Soc. 1876, p. 457. 



