58 CETACEA. 



Delphinus, Linn. ; Illiger, Prod. 143, 1811. 



Delphinus and Monodon, Cuv. Tab. Elem. 17-98. 



Delphinidse, Gray, Ann. Phil. 1828; Spic. Zool. i. 1828; Cat. 



Mam. B.M. 104 ; Zool. Erebus fy Terror. 



Delphinidfe and Monodontidae, Gray, L. Med. Rep. xv. 310, 1821. 

 Cete, pars, Illiaer. 

 Delphinidse, Delphinina and Monodontina, Selys Longchamps, 



1842. 



Les Ce'tace's piscivores et les Narwals, F.Cuv. D. S. N. 1829. 

 Zahnwale, pars, Oken, Lehrb. Naturg. 672, 1815. 



This family is easily known from the Toothed Whales, or Ca- 

 todontidae, by the smaller and more proportionate head ; and in 

 those species which have lost their upper teeth at an early age, 

 by there being no regular series of pits in the gum of the upper 

 jaw for the reception of the teeth of the lower one ; and also by 

 the hinder part of the skull not being deeply concave, and sur- 

 rounded on the sides and behind by a high ridge. 



These animals when first born are large compared with the 

 size of the parents (according to Dr. Knox, the fcetus of the por- 

 pesse is half the length, that is, one-fourth the size of the parent 

 before it is born (Trans. Roy. Soc. Edin. ii. 208) ; and they ap- 

 pear to attain their full size very rapidly, which may account for 

 the very slight difference to be observed in the size of the skull, 

 and the great uniformity in the number, and in the space which 

 the series of teeth occupy upon the edge of the jaws in the different 

 specimens of the same species. Hunter thought the exact number 

 of teeth in any species was uncertain : observing the teeth in the 

 middle of each series were the largest and the most firmly fixed, 

 he states his belief that " the jaws increase posteriorly and decay 

 at the symphysis, and while the growth is going on, there is a 

 constant succession of new teeth, by which means the new-formed 

 teeth are proportioned to the jaw." Phil. Trans. 1788, 398. 

 Dr. Fleming, from the examination of the jaws of two porpesses 

 of different ages, thinks " the jaws lengthen at the symphysis and 

 at the base ;" and that " the new teeth formed at these places are 

 the smallest, and that there is no absorption." Fleming, Phil. 

 Zool. ii. 208. This may be the case with the specimens before 

 they arrive at their full size ; but no skull of this kind has fallen 

 under my observation : and as far as my experience will carry 

 me, the numbers, size, and disposition of the teeth furnish the 

 most important characters for the determination of the species 

 and the definition of genera. M. F. Cuvier's remarks (Cetac. 

 103, 104) on the teeth as the characters of genera are not con- 

 sistent with my observations, for they appear quite as charac- 

 teristic of the different genera as those of other orders of Mam- 



