OCR Text |
Show 1893.] CETACEAN GENUS MESOPLODON. 229 the premaxillary thickening 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 individual 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 Delphinidce, and can, therefore, be of little value as a character for differentiating the species. The anterior 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 DENSIROSTRIS (Blainville). Belphinus densirostris, Blainv. Nouv. Diet. d'Hist. Nat. ed. 2, t. ix. p. 178 (1817). Mesodiodon densirostris, Duvern. Ann. des Sc. Nat. ser. 3, t. xv. p. 59 (1851). Ziphius sechellensis, Gray, Zool. E. & T. p. 28 (1846). Ziphius sechellensis, Krefft, P. Z. S. 1870, p. 426. Biplodon densirostris, Gervais, Zool. et Pal. frangaises, ed. 1, t. ii. expl. no. 40 (1850); Ann. des Sc. Nat. ser. 3, t. xiv. p. 16 (1850). 6. MESOPLODON GRATI (Haast). Oulodon grayi, Haast, P. Z. S. 1876, pp. 7 & 457. Mesoplodon knoxi, juv., Hector, Tr. N . Z. I. v. p. 168 (1873). Mesoplodon hectori, Gray, Haast, Tr. N . Z.I. ix. p. 455 (1877). Mesoplodon australis, Flower, Tr. Z. S. x. p. 419 (1878). Mesoplodon hectori, Gray, Hector, Tr. N . Z. I. vi. p. 86 (1874); vii. p. 362 (1875). |