THE MAMMALIA OF THE DEEP KJVEIi BEDS. 99 



Lower fourth premolar, length ' 022 



Lower fourth premolar, width 014 



Lower molar series, length 070 



Lower first molar, length 023 



Lower first molar, width 014 



Lower second molar, length 022 



Lower second molar, width 012 



Lower third molar, length 025 



Lower third molar, width 010 



Upper median incisor, width 011 



Upper second incisor, width 010 



Upper third incisor, width 009 



Upper molar-premolar series, length 147 



Upper premolar series, length 083 



Upper first premolar, length 014 



Upper first premolar, width 01 1 



Upper second premolar, length 025 



Upper second premolar, width 025 



Upper third premolar, length 025 



Upper third premolar, width 027 



Upper fourth premolar, length 025 



Upper fourth premolar, width 026 



Upper molar series, length 068 



Upper first molar, length 025 



Upper first molar, width 028 



Upper second molar, length 025 



Upper second molar, width 027 



Upper third molar, length 021 



Upper third molar, width 022 



The discrepancy between the measurements of individual teeth and the totals of the molar and premolar 

 series is due to overlapping. 



I know of no materials which would render possible a detailed comparison of 

 the skull structure of this species with that of A. aurelianense, the European speci- 

 mens which have been figured being extremely imperfect in this respect. Some 

 points of interest may, however, be determined. In the European species the orbit 

 occupies the same position as in the American, but the infraorbital foramen is 

 slightly farther forward. The zygomatic arch appears to have a less abrupt descent 

 anteriorly and the base of the cranium to be less elevated. The premaxillaries are 

 very different in appearance ; the alveolar portion is shallower and the symphysis 

 shorter and devoid of the conical elevation at the top; it is also of more uniform 

 depth and its upper margin does not show the abrupt descent above the diastema 

 which is so characteristic of A. equinum. The horizontal ramus of the mandible is 

 deeper and the rise of the inferior margin at the symphyseal portion and the chin 



