1044 On the genus Hexaprotodon. [Dec 



canine teeth is four inches in breadth, the whole being- comparatively 

 flat and broad : the reverse of what belongs to the species of which I 

 supposed it might have been a young individual. The specimen is 

 however too imperfect to show any peculiarities of dentition, the sockets 

 of some of the teeth only remaining, and the left angle of the jaw being 

 broken so as to give the muzzle an unequal appearance. 



It is not consistent perhaps with the most approved method of study- 

 ing nature, to lay very great stress on the peculiarities of any one organ 

 in different animals ; but it is rare that more than a fragment of some 

 portion of the skeleton of fossil vertebrata is afforded for observation. 

 The development of horns, and even of some parts of the frontal bone, 

 as of the superciliary arches of the orbits, is liable to sexual and indi- 

 vidual peculiarities*, but I am aware of no such objections to the full- 

 est reliance on the lower jaw as a safe criterion for specific variations ; 

 for this purpose I have made considerable use of it in the arrangement 

 of fishes, and there is no reason why it might not be equally useful as a 

 criterion of species in other classes. 



The two species described by Dr. Falconer and Captain Cautley 

 differ essentially in this, that the jaw of H. Sivalensis is broad at the 

 muzzle, and contracted more than the existing species over the penul- 

 timate false molar (Asiatic Researches, XIX. 47.) while that of H. 

 Dissimilis is very narrow at the symphysis, where a greater number 

 than four incisors does not appear to have existed. Hence fig. 4 in 

 the annexed plate, and figs. 1, 2, plate IV. Asiatic Researches, XIX. 

 represent H. Sivalensis, while the imperfect fragment in Colonel Col- 

 vin's collection fig. 3, in the annexed plate, is a characteristic frag- 

 ment of H. Dissimilis of Falconer and Cautley. 



But still we have fig. 4, pi. IV. (As. Res. XIX.) of Durand, which 

 corresponds with a very perfect lower jaw in Colonel Colvin's col- 

 lection, from which my fig. 5, on the annexed plate was taken, and 

 regarding which Mr. Durand justly observes (Op. Cit. pp. 57) r " It 

 presents a marked difference in the shape of the incisors which are 

 more elliptical than in the preceding varieties. The exterior incisors 

 have a section not observable in any other specimen ; and are rela- 

 tively to the four centre incisors set lower than analogous incisors of 

 other varieties — may not this" he continues " be considered a distinct 

 species ?" I am led to the conclusion after an examination of Colonel 

 Colvin's specimens and all others in our museum that it is, and pro- 



* In one of Major Hay's beads of the hippopotamus the arches of the orbits 

 ascend two inches above the most prominent part of the intervening nasal pro- 

 cess, and in the other only one inch. 



