58 CETACEA. 
Delphinus, Linn.; Illiger, Prod. 143, 1811. tae | 
Delphinus and Monodon, Cuv. Tab. Elem. 1798. (| 
Delphinide, Gray, Ann. Phil. 1828; Spic. Zool. i. 1828; Cat. 
Mam. B.M. 104; Zool. Erebus & Terror. a: 
Delphinide and Monodontide, Gray, L. Med. Rep. xv. 310, 182) 
Cete, pars, Illiger. ol 
Delphinide, Delphinma and Monodontina, Selys Longchamp: 
1842, 
Les Cétacés piscivores et les Narwals, F. Cuv. D. S. N. 1829. — 
Zahuwale, pars, Oken, Lehrb. Naturg. 672, 1815. 4 
This family is easily known from the Toothed Whales, or Ca 
todontide, by the smaller and more proportionate head; and 1 
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 uppe 
jaw for the reception of the teeth of the lower one ; and also by 
_ the hinder part of the skull not bemg deeply concave, and sur 
rounded on the sides and behind by a high ridge. a 
These animals when first born are large compared with th 
size of the parents (according to Dr. Knox, the foetus of the por. 
pesse is half the length, that is, one-fourth the size of the paren 
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 numk 
of teeth in any species was uncertain : observing the teeth in th 
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 isé 
constant succession of new teeth, by which means the new-formet 
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 ant 
at the base ;”’ and that “the new teeth formed at these places ar 
the smallest, and that there is no absorption.”—Fleming, Phil 
Zool. ii. 208. This may be the case with the specimens befor 
they arrive at their full size; but no skull of this kind has falle 
‘under my observation: and as far as my experience will ry 
me, the numbers, size, and disposition of the teeth furnish th 
most important characters for the determination of the specie 
and the definition of genera. M. F. Cuvier’s remarks (Cetae 
103, 104) on the teeth as the characters of genera are not con 
sistent with my observations, for they appear quite as chara 
teristic of the different genera as those of other orders of Mam 
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