THE MAMMALIA OP THE DEEP RIVER BEDS. 149 



belongs to Merychyus. It may be provisionally referred to M. pariogonns Cope, 

 though unfortunately a comparison with the type specimen is of little service, for the 

 two skulls have almost nothing in common. In the type specimen, the cranium and 

 molar teeth are preserved ; in the specimen before us, only the face. The teeth are in 

 such different stages of wear in the two specimens that they may or may not pertain 

 to different species. Almost certainly it cannot be referred to M. zygomaticus, from 

 the type of which it differs in its smaller size and less pronouncedly hypsodont 

 dentition. 



The incisors, canines and first premolar in the upper jaw are represented only by 

 alveoli, but these show that the canine was rather slender and was followed with hardly 

 an appreciable diastema by p. 1 , which was implanted by two distinctly separated fangs, 

 the anterior one of which is considerably larger than the posterior. The second pre- 

 molar has almost plane external face, with no median ridge and only the faintest 

 trace of a cingulum. The crown is so much abraded that only a small enamel invag- 

 ination on the inner side of the tooth remains visible. So far as can be judged from 

 its present worn condition, the construction of pjs is very much the same as that of 

 p^s, but with a more prominently developed deuterocone. As in the genus, and 

 indeed the family, generally, M consists of two crescents ; a difference from the 

 species of the upper Loup Fork is to be found in the strongly developed internal 

 cingulum. 



The molars increase in size from m. 1 to m. 3 ; they appear to be as brachyodont 

 as in the type specimen, though this may be due, in part at least, to their abraded 

 condition. The external pillars (para- and mesostyles) are less prominent than in 

 M. zygomaticus. 



The face has not attained that great vertical depth in the region of the orbits 

 which is characteristic of M. zygomaticus ', the orbit is more oval in shape and more 

 oblique in position than in that species and is notched superiorly ; the forehead is 

 more inflated by the sinuses. There are no supraciliary ridges, and the sagittal crest 

 must have commenced at a point considerably farther back than its origin in Mes- 

 oreodon. The malar is not so heavy as in M. zygomaticus, and the masseter ridge is 

 continued well forward upon the maxillary, which displays a slight facial depression 

 above p^s and pJ*. The infraorbital foramen is double; the antero-superior foramen 

 is above pJ5 and the postero-inferior opening above the space between p_3 and M. 

 The lachrymal is large and has an extensive but not very deep depression. A facial 

 vacuity was obviously present between the maxillary, lachrymal and frontal, but its 

 size and shape cannot be determined, as none of the bones mentioned have complete 

 margins and the nasals are entirely lost. The anterior nares arc low, very much nar- 



