5 



DlNOCERATA. 



The genera of this* group known to the writer are four, which differ 

 as follow : 



1. Nasal bones with flat horizontal horn-cores overhanging their apex. 

 Cervical vertebrae short ; malar bone much reduced in 



front Loxolophodon. 



2. Nasal bones with small tuberosities. 



Cervical vertebrae short Bohasileua. 



Cervical vertebrae longer; the malar bone reaching maxil- 

 lary face Uimatherium. 



3. Nasal bones without the anterior horn-cores. 



Cervicals ? Megacer-atops. 



The dentition of this group requires special notice. Judging from the 

 relative sizes of the teeth, I have written the molar series of Loxoloplio- 

 don 4 2, but judging from the forms of the crowns, it should be 1 5. 

 However this should be, I have no doubt that as in other Proboscidia the 

 premolar and not the molar series is deficient, and that there are three 

 or four true molars at least. In a mandible found alone, which agrees in 

 size with some species of Uintatlierium, six molars are preserved. Of 

 these the posterior two display three sub-transverse crests, of which the 

 anterior two form a chevron with open apex directed to the inside. An- 

 terior to the front crest is a cingular tubercle. The symphyseal part of 

 the jaw is remarkable : it is coossified, exceedingly compressed, and 

 curved upwards so as to resemble slightly the narrow prow of a South 

 Sea boat. There are two teeth on each side, which are separated from 

 the molars by a diastema. They are much compressed and curved up- 

 wards and forwards, and the anterior pair issue from the jaw in contact. 

 The crowns are lost in the specimen. The determination of these teeth 

 is facilitated by the presence of the mental foramen below the posterior 

 one. This foramen issues, as is well known, posterior to the canines in 

 all mammalia, and either below premolars, or the diastema. The two 

 teeth in our fossil will then be premolar and canine respectively, and the 

 incisors must be regarded as wanting. This is in conformity with the 

 structure of the upper jaw, and is rendered probable by the great reduc- 

 tion of the symphysis of the lower jaw in the species. It is also suggested 

 by the almost universal tendency to reduction of the incisors seen in the 

 mammals of the same extinct fauna. In Bathmodon and Palceosyops the 

 canines are thrown into the incisor series as in Ruminantia, and in Palcc- 

 osyops the outer incisors are much reduced. In several genera there are 

 but two incisors. Finally in Synoplotherium, and probably*in Anchipho- 

 dus, the large inferior teeth described by Dr. Leidy and myself as in- 

 cisors and which resemble the cutters of Rodentia, are immediately in 

 front of the mental foramen, and bear the same relation to it and to the 

 premolar teeth, as do the canines of Palceosyopa and other mammalia. 

 Hence I believe these to be canines, and that the inferior incisors are 



