■G. T. BETTANY ON THE GENUS MERYCOCHffiRUS. 261 



The following is given as a brief definition of the family Oreo- 

 dontidae : — 



Hornless Ungulates, in which the posterior region of the skull 

 presents a strong sagittal crest flanked by large temporal fossae. 

 Orbits closed. Zygomatic arches strong. No unossified spaces on 

 the side of the face. Teeth 44, a complete series. Canines large, 

 the lower being transformed premolars. Molars of typical rumi- 

 nant form. 



The following more extended definition is copied, for convenience 

 of reference, from the " Extinct Mammalian Fauna," p. 71. 



" Oreodontid^:. The skull has somewhat the form of that of the 

 peccaries ; the cranial portion especially resembles that of the camel. 

 It is hornless. The temporal fossae are large, and separated by a 

 median sagittal crest as in the camel. The zygomatic arches are 

 strong. The orbits are closed behind by an arch. Large and com- 

 paratively deep fossae impress the lachrymal bones in advance of the 

 orbits. No unossified spaces occupy any part of the face. The 

 auditory capsules are variable in degree of development. The para- 

 mastoids are long and strong. The lower jaw is broad and deep 

 posteriorly, and impressed with a comparatively deep fossa below 

 the lunar notch. The teeth in both jaws form nearly unbroken 



arches. The formula of dentition is i. ==, c. ==, pm. g^, m. — 



= 44 ; well-developed incisors in both jaws, the fourth of the lower 

 jaw being a transformed canine, as in ordinary ruminants. Canines 

 well developed and strong in both jaws, suilline in their resem- 

 blance, those of the lower jaw being transformed premolars. The 

 anterior three premolars having the crown in the form of a demi- 

 cone, with more or less rudimental elements at the base internally. 

 The fourth upper premolars and the true molars of both jaws con- 

 structed after the ordinary ruminant type, and most nearly resem- 

 bling in form those of the Deer family." 



This description may be supplemented and modified by observa- 

 tion of our specimens as follows : — In the first place, the general 

 resemblance to the skull of the Peccary is very much less strong in 

 the larger species than in the smaller. The temporal fossae are in 

 some very large, and the median sagittal crest may be very strong 

 and prominent. The only breaks in the series of teeth are those 

 caused by the protrusion of the large canine teeth in each jaw into 

 corresponding intervals in the series of teeth in the other jaw. It 

 is better to amend the dental formula according to the definition 

 which defines the canine of the lower jaw as the tooth which bites 

 in front of the first tooth in the superior maxillary bone; the first 

 premolar in the lower jaw of Oreodontidae will then be called a 

 caniniform premolar. Thus we get the normal dental formula, so 

 frequently met with in early Mammalia, 



. 3—3 1—1 4—4 3—3 . . 



*■ 3=3' C - 1=1' P™" 4=4' m - 3=3 = 44 - 



The suilline resemblance attributed to the canines should be omitted, 



