418 



PilOF. W. H. FLOWER ON THE GENUS MESOPLODON. 



mandible, as in M. 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 M. 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 M. 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 M. hectori the apex of the 

 tooth in the young animal is directed forwards. In M. hidens the apex of the tooth is 

 at first directed backwards, but during growth becomes rotated forwards. In the only 

 specimen of M. europceus known (an adult) the apex of the tooth is directed somewhat 

 forwards. 



These characters may be thus placed in a synoptical form : — 



Lateral 



Prsemaxillary 



Position of 



Other dental characters. 





groove. 



maxillary. 



mandibular tooth. 









Level. 



Close to apex of 

 mandible. 























M. europceus. 







dibular sym- 









physis. 







Absent. 



Level. 



Near hinder edge 

 of mandibular 

 symphysis. 



Apex of tooth at first di- 

 rected backwards, and 

 during growih rotated 

 forwards. 9_ 



M. hidens. 



Slight. 



Level. 



Ditto. 



Apex of tooth^Pifcted and 

 mounted tm a.%fl.&ftmwd 

 base, whien increases m,- 

 length with age, and 

 finally curves round the 

 maxilla. 



M. layardi. 



Deep. 



Behind. 



Ditto. 



Apex of tooth vertical. Al- 

 veolar portion of jaw 

 expanded. 



M. densirostris. j 



Deep. 



Behind. 



Ditto. 



Apex of tooth vertical. A 

 row of small teeth in 

 upper jaw. 



M. grayi. 



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 communication is based are : — 

 1. The skull of a young specimen of M. hectori, the type and at present only known 

 example of that species. 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. hi. 1870, pis. xiv. 



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