414 CETACEA. 



short way beyond its base, but immediately expands, and then gradually contracts, 

 the outline of the premaxillaries having much the same contour as that of the 

 maxillaries. 



Teeth.— There are fewer teeth in the lower than in the upper jaw, there being 

 always two to three less in the former, and the lower are larger than the upper teeth. 

 The maximum number of teeth observed by me has been 17 in the upper jaw 

 associated with 14 teeth in the lower jaw on each side, and the minimum number 

 14 in the upper and 12 in the lower jaw. The number of teeth on the two sides of 

 the skull is liable to variation, 15 occurring on one side and perhaps 17 on the 

 other, and the same may take place in the lower jaw, subject, apparently, to a 

 maximum of 14 on both sides. In 0. brevirostris the teeth vary from 15 to 17 

 in the upper jaw and from 12 to 14 in the lower jaw. One individual has |4r4nl 

 and another |4fJ^^ 



The premaxillaries have each one tooth near the external margin of their tips, 

 and in tliis respect Orcella resembles Orca. In the foetus in which the teeth had 

 their points still covered by the gums the diameter of a tooth did not exceed 

 0"-07, whereas the same tooth in the mother had a diameter of 0"-20. The teeth 

 are rather sharply conical, and their crowns are slightly inclined inwards, but 

 with use they become perfectly flat. In an adolescent O. brevirostris the teeth 

 are unworn, but in an adult they are much worn away, especially the eight 

 hindermost teeth, but the remaining portions of these teeth have much greater 

 diameter than the corresponding portions of the same teeth in the adolescent. 



The hyoid apparatus has the usual delphinoid character. 



Conclusion.- — The form of the skull of Orcella, the character of its teeth, the 

 relation of its ribs to the vertebral column, the features of the latter generally, 

 the well ossified sternal ribs, and the presence of a dorsal fin, — all indicate it to be 

 a member of the family Delphinidce. The sub-division of the Delphinidce into 

 natural groups, however, as has been remarked by Professor Elower\ is by no means 

 easy, and we must either make as many sub-families as there are genera or group 

 them together into one family. Professor Heiuhardt^ also, in remarking on the 

 systematic position of Fseudorca, contended that to regard Orca as a division among 

 the toothed whales of more than generic worth, as a group or family by themselves, 

 as had been suggested by Eschricht, was neither sound in itself nor indeed supported 

 by any defensible reason, and what was true of Orca in this respect was equally 

 applicable to Globicephalus, Grampus, Lagenorhynchus, Thoccena, 8fc. Dr. Gray, 

 however, followed an entirely different course, as he elevated Grampus, Globicephalus, 

 and Orca into as many distinct families, and the Delphinidce he sub-divided into 

 five tribes, but as Professor Plower further remarks, the genera so blend one into 

 the other that it is difficult neatly to define their distinguishing characters, and each 

 new discovery of a Delphinoid Cetacean seems to lend more weight to these opinions. 



' Trans. Zool. Soc. 1869, vol. vi. p. 114. 



- Oversigt. over Kong. Danske, Vidensk. Selsk. Forhand. 1862 ; Transl. Ray Soo. 1866, p. 218. 



