OF THE CHINESE WHITE DOLPHIN. 155 



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 B. sinensis, as indicated by the 

 alveoli, are pEsf* 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 yq", apparently by erosion or absorption of the surface. 



The characters of the mandibular teeth are well shown hi the detached jaw of the 

 younger specimen, as they are nearly all perfect and in 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. 



Entire length 1-00 



Length of crown . . 0"35 



Length of crown and portion of root projecting above alveolar 



margin of jaw 0*50 



Greatest (transverse) diameter of root 0-20 



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. 



