HOLLAND AND PETERSON: OSTEOLOGY OF THE CHALICOTHEROIDEA. 245 
THe DENTITION. 
(Plates XLVIII-LIII.) 
The Superior Dentition. 
(Plates XLVIII, XLIX, and LI.) 
The absence or presence of superior incisors in Moropus cannot now be defi- 
nitely determined. The premaxillary bone has not been found in any specimens 
thus far recovered, and we have yet to learn whether the wear of the median lower 
incisors is caused by meeting a median upper pair, as represented om the model 
(see Plate LIII), or whether this abrasion is caused in some other way. ‘There is 
no superior canine, as shown by skull No. 1707. The long edentulous premaxillary- 
maxillary border is succeeded by a series of large teeth covered with thick enamel 
and implanted in the jaw by long powerful roots. The archaic Perissodactyl type 
and structure of these cheek-teeth is recognized, and it is with Palewosyops and 
Titanotherium that they have generally been compared. The structure and modi- 
fication, especially of the premolars, is, however, quite different from that of the 
latter genera and merely indicates a parallelism. P! is absent, as is also the case 
in the known European and Asiatic forms. P? is triangular in general outline, the 
proto- and tritocones have united to form a solid ectoloph in the formation of 
which the protocone plays the most prominent part, forming the apex of the 
external wall without dividing this portion of the crown by a transverse valley as 
seen in Titanothertum and many other Perissodactyls. On the antero-internal 
angle the cingulum has developed into a protoloph of considerable functional 
importance, which in earlier Kuropean forms, e. g., Schizotherium priscum, appears 
to be wanting so far as is known. This is also true of Chalicotherium goldfusst. 
The metacone is much more developed, and, on further wear, is connected with 
the ectoloph as a broad functional metaloph, somewhat as seen in the Rhinocerotide, 
including the median cross-valley which separates proto- and metalophs. The 
metaloph is surrounded by a heavy cingulum, which continues forward to form 
the protoloph already described. The latter appears to have a varied development 
in different individuals. Externally the tooth has little or no cingulum. P? differs 
from the preceding tooth (1) by being more quadrate in general outline, (2) by 
having one instead of two tubercles. As in the tooth previously described, the 
ectoloph presents a broad transverse surface on the grinding face. The ectoloph 
is separated from the internal cone (deuterocone) by a wide longitudinal valley 
and a deep pit. The deuterocone itself is very prominent and sometimes has 
