PEOF. W. H. FEOWEE ON THE GENUS MESOPLODON. 417 



Bsrardius hectori, Gray, Annals & Mag. N. H. ser. 4, vol. viii. p. 117 (1871). 

 Mesoplodon knoxi, Hector, Trans. New-Zeal. Inst. vol. v. p. 167 (1873). 



Hab. Titai Bay, New Zealand. Very young; length 9' 3", 1866 (Knox and Hector). 



6. M. grayi, Haast, Proc. Zool. Soc. 1876, p. 7. 

 Oulodon grayi, Haast, P. Z. S. 1876, p. 457'. 

 Hab. New Zealand. 



These six species do not differ greatly in size, and present a close family or, rather, 

 generic resemblance ; but still there are certain cranial and dental characters by which 

 the skulls can readily be distinguished. 



The most easily recognized of these are : — 



a. In some species there is a deep lateral longitudinal groove at the base of the 

 rostrum, commencing posteriorly in a blind pit below the tubercle of the maxilla 

 situated in front of the anteorbital notch, and bounded above and below by sharply 

 defined prominent ridges, both formed by the maxilla. This groove characterizes 

 M. grayi and M. densirostris. No trace of this groove, but a prominent ridge instead, 

 which gives a wide base to the rostrum, as seen from above or below, exists in 

 M. Helens, M. europceus, and M. hectori. The groove is slightly developed in M. layardi, 

 which in this respect presents an intermediate condition. 



b. The relative position of the foramina for the exit of the facial branches of the 

 second division of the fifth nerve appears to afford constant distinctive characters between 

 certain of the species. The principal foramina are in two pairs : — 1, the larger or more 

 external, situated in the maxilla, and often double, corresponding to the infraorbital 

 foramen in man (Plate LXXI. mf) ; and, 2, the smaller and nearer the middle line, 

 situated in the prsemaxilla (pf). The latter are rather in front of, or on the same level 

 with, the maxillary foramina in M. bidens, M. europceus, M. hectori, and M. layardi, and 

 placed decidedly on a posterior level in M. densirostris and M. grayi. 



c. The constant presence of a row of small teeth in the upper jaw is said to dis- 

 tinguish M. grayi from the other species, though, as will be discussed presently, this 

 can scarcely be considered of generic importance. 



d. The position of the large tooth in the lower jaw, whether close to the apex of the 



1 In the notice of this paper in the Proceedings of the Zoological Society, 1877, p. 684, for 

 " 7. M. Jiaasti,n. sp present memoir," read: — 



7. M. haasti, n. sp. 

 Hab. New Zealand. 



Known only hy a portion of a cranium in the Museum of the Royal College of Surgeons. 



8. M. australis, n. sp. = M. hectori (Gray). Hector, Trans. New-Zealand Inst. vol. vi. p. 86, and vol. vii. 

 p. 362. 



Hab. New Zealand. 



A complete skeleton, now in the British Museum, described in the present memoir. 



3l2 



