Or 
OF THE CHINESE WHITE DOLPHIN. 15 
The petrotympanic bones resemble those of other members of the genus. The 
greatest length of the scroll-like tympanic is 1'"45, its greatest breadth 0-85. 
The numbers of the teeth of the adult specimen of D. sinensis, as indicated by the 
alveoli, are = total 128. In the second lower jaw there are 32—33. In the former 
they are unfortunately very incomplete; and as those that remain have mostly fallen from 
their sockets, and been artificially replaced, absolute reliance cannot be placed upon their 
present position in the jaws. Many of them, both in the maxilla and mandible, are 
worn down to flat-topped stumps, which can have scarcely projected above the level of 
the gum, all of the crown and a portion even of the root having disappeared. Such a 
mode of wear occurs habitually in D. tursio, but I have never observed it in any other 
of the numerous species of Dolphins. The amount of truncation varies in extent in 
different parts of the jaw; it affects the lower more than the upper teeth. Those in 
the posterior part of the maxilla have entirely escaped. Besides the truncation of the 
apex, many of the upper teeth, especially near the hinder part of the series, have the 
neck, or that part of the root immediately adjoining the enamelled crown, suddenly 
contracted for a space of about +'5'', apparently by erosion or absorption of the surface. 
The characters of the iain batak teeth are well shown in the detached jaw of the 
younger specimen, as they are nearly all perfect and im situ. ‘Truncation of the apex 
has commenced in nearly all; but the greater number are but slightly affected, and in 
none is so much as half the crown worn away. The roots of the teeth are much 
thicker than the crowns, they are slightly flattened from before backwards, and taper 
upwards to a sufficiently well-marked “neck,” above which is the smooth, enamelled, 
conical, slightly compressed (from before backwards) and incurved crown. In the 
posterior fourth of the ramus the teeth are placed vertically, but in the remaining 
portion they incline considerably outwards; the three or four most anterior are again 
more vertical. Except those at the extreme ends of the series, which, as usual, are 
somewhat smaller than the others, the teeth of the lower jaw do not differ materially 
from each other in size. The following are the dimensions of an unworn tooth from 
near the middle of the series. 
inch. 
Iai Meee eet er aka Bae of ve Fs et on 4 OD 
Length ofcrown . . . . ; es : ; 0°35 
Length of crown and portion of root projetng above alveoli 
margin ofjaw .. . Tor eh aaa amr ter IGN) 
Greatest (transverse) demetey of TOOt@ the se ene ete? tee LAO) 
Greatest (transverse) diameter of crown . . . . . . . 0°23 
The teeth are placed at very regular distances, their roots being completely separated 
by a very narrow strip of alveolus. As nearly as may be, three teeth occupy each inch 
of the alveolar border. 
