1893.] CEXACEAIS' GENUS MESOPLOBOjS'. 229 



the premaxillary thickeuiug was very strongly marked more 

 posteriorly, and the vomerine upgrowth, it could be seen, had 

 lain between them and had evidently been squeezed into a very 

 narrow plate in the centre. It is apparent that the basirostral 

 groove here was better developed than in more aged individuals. 

 It commenced posteriorly, as in M. grayi, in a deep blind pit 

 under the maxillary tubercle and ran forward, well marked, on 

 the strongly- developed buttress already formed by the pterygoids, 

 palatines, and maxillaries. It gradually vanished as the maxillary 

 descended from the upper face of the rostrum. In this indi- 

 vidual the palatines extended forward for a long way beyond 

 the extremity of the pterygoids, as well as appeared on their 

 inner side to within half an inch of their apices, during which 

 short space only the pterygoids lay on the maxillaries. In Van 

 Beneden's figure, however, in his ' Osteographie,' the palatines 

 do not extend forward beyond the extremity of the pterygoids ; 

 while in the Canterbury Museum specimen, and in the young 

 example figured by Sir W. Turner, they protrude for 1^ inch in 

 front, as well as extend beyond them all round. It is evident 

 that in Mesoplodon the relations of the pterygoid and palatine bones 

 are not so constant as in the Dtlphinidce, and can, therefore, be of 

 little value as a character for differentiating the species. The an- 

 terior end of the fossa of the pterygoid in the ' Challenger ' and 

 British Museum examples, just referred to, extends far forward of 

 the line through the anterior edge of the maxillary tubercles — a 

 constant character apparently in M. layardi. 



The centre of the tooth in the mandible of the specimen in the 

 Colonial Museum, Wellington, was situated 2-3 inches anterior to 

 the posterior edge of the symphysis. 



5. Mesoplodon DENSiEOSTKis (Blainville). 



DelpJiiniis densirostris, Blainv. Nouv. Diet. d'Hist. Nat. e'd. 2, 

 t. ix. p. 178 (1817). 



Mesodiodoti densirostris, Duvern. Ann. des Sc. Nat. ser. 3, t. xv. 

 p. 59 (1851). 



Ziphins sechcllensis, Gray, Zool. E. & T. p. 28 (1846), 



Ziphius sechcllensis, Krefft, P. Z. 8. 1870, p. 426. 



Diplodon densirostris, Gervais, Zool. et Pal. francjaises, ed. 1, 

 t. ii. expl. no. 40 (1850) ; Ann. des Sc. Nat. ser. 3, t. xiv. p. 16 

 (1850). 



6. Mesoplodon geayi (llaast). 



Oulodon fjraiji, Ilaast, P. Z. S. 1876, pp. 7 & 457. 

 Mcsopjlodon Ino.vi, juv.. Hector, Tr. N. Z. I. v. p. 168 (1873). 

 Mesoplodonhedori, Gray, Ilaast, Tr. IS. Z.I. ix. p. 455 (1877). 

 Mesoplodon auslrcdis, Flower, Tr. Z. S. x. p. 419 (1878). 

 Mesoplodon heclori, Gray, Hector, Tr. N. Z. I. vi. p. 86 (3874); 

 vii. p. 362 (1875). 



