246 MEMOIRS OF THE CARNEGIE MUSEUM. 
well-defined ridges of enamel extending from the base of the tubercle to the apex. 
There is a well-developed cingulum which is visible near the antero-external angle 
of the ectoloph and continues to the internal face of the deuterocone, where it 
sends a heavy fold to very nearly the apex, thence continuing again to the postero- 
external angle of the ectoloph. Externally the cingulum is not nearly as promi- 
nently developed. P*is slightly larger than the preceding tooth, while the structure 
is otherwise very similar. The antero-external angle of the ectoloph is generally 
more developed in the last premolar, and there is usually also found a more promi- 
nently developed ridge of enamel from the apex of the protocone some distance 
up on the external face of the tooth. The deuterocone and the cingulum are 
developed in the same proportion as in the preceding tooth. The cheek-teeth 
gradually increase in size toward the back of the jaw. The premolar series takes 
up less than one-half of the space which is occupied by the molars, thus differing 
entirely from conditions found in the Perissodactyla in general, where the length 
of the premolar and molar series is more nearly subequal. In the European 
Schizothervum priscum from the phosphorites of Querey (Oligocene) the premolars 
occupy relatively a greater space. 
M' is much enlarged, more especially in the antero-posterior direction. The 
general configuration of the crowns is as suddenly changed from that of the pre- 
molars as is the size. The external face of the ectoloph suddenly takes on the 
W-shaped form so characteristic of the molars of the Titanotheriide with which 
those of the Chalicothervide have often been compared. The metacone is a large 
bunodont tubercle with an external exit of the cross-valley in front and back of it. 
The anterior face has a very prominent and rather smoothly rounded cingulum, 
which continues inwards and backwards and terminates at the exit of the anterior 
cross-valley. The posterior cross-crest is divided into an outer and inner lobe 
separated by a postfossette. On M! this fossette is generally very soon obliterated 
by wear, the crest being often entirely bisected so as to form a valley between the 
ectoloph and the hypocone. At the posterior base of the metacone there is usually 
a smoothly rounded cingulum extending downward toward the exit of the posterior 
cross-valley. Posteriorly the cingulum forms a shelf at the exit of the postfossette, 
while at the base of the ectoloph there is a light cingulum. M7? is one-fifth longer 
than the tooth just described. The fold of the ectoloph is more conspicuous, 
the postfossette is deeper, the posterior face more backwardly extended, and the 
ledge-like cingulum broader than on M?'; otherwise there are little or no differences 
in the general construction of the two teeth. M? is only very slightly longer than 
the preceding tooth, but otherwise there is little or no difference in the configuration 
of the crowns. 
