372 DOLPHINS CHAP. 
can leap right out of the water, and while in the air can turn its 
head from side to side, a capability which has not been mentioned 
in any other Whale. It can also stay under water for an unusually 
long period. Captain Gray,’ who has made an accurate study of 
this species, states that so long a period as two hours is the linit of 
endurance; this event occurred in the case of a harpooned Whale. 
Fam. 2. Delphinidae.—This family, which includes the 
ereater number of Cetacea, may thus be characterised :—Whales 
of small to moderate size. Teeth as a rule numerous, and 
present in the upper as well as in the lower Jaw. Maxillae 
without large crests; the pterygoids, often meeting in the middle 
line, enclose an air space open behind. The anterior (five to eight) 
ribs are two headed, the posterior with tubercular head only. The 
sternal ribs are ossified. 
The Dolphins and Porpoises, as already stated, embrace the 
greater number of existing species of Whales. Sir W. Flower and 
others who have followed him, allow nineteen genera. But as to 
the exact number of known species there is much uncertainty. 
That very careful observer, Mr. True, considers” that there are 
fifty which demand recognition. As many as one hundred have 
received names. The matter is one which is perhaps barely ripe 
for decision. All the Dolphin tribe are, for Whales, smallish 
animals. The Killer Whale, Orca, is the only genus (or species ?) 
which usually attains to more than moderate bulk. The rather 
mysterious Delphinus coronatus, 36 feet in length, of M. de Fré- 
minville, would seem to be a Ziphioid; it was described as having 
a very pointed beak, and as having the dorsal fin situated near 
the tail; such characters suggest a MJesoplodon. 
The genus Delphinapterus, the Beluga or White Whale, con- 
sists of but a single species, though as usual more than one 
name has been given to supposed different species. It is char- 
acterised as a genus by the following assemblage of structural 
features :—It has only eight to ten teeth occupying the anterior 
part of the jaws only. All the cervical vertebrae are free and 
unjoined, The vertebral formula is -C 7, D 11 (or 12), L 9, 
Ca 23. The pterygoids are wide apart, though they converge 
as if about to meet at their posterior ends. There is no dorsal 
fin. The colour is white. 
1 Proc. Zool. Soc. 1882, pp. 722, 726. 
2 Bull. U.S. Nat. Mus. No. 36, 1889, p. 7. 
