242 MEMOIRS OF THE CARNEGIE MUSEUM. 
moreover, the different processes are heavier than in Moropus. The postglenoid 
process in Macrothertum is more rounded, while in Moropus it possesses a greater 
transverse and a less antero-posterior diameter. The tympanic bulla in Macro- 
thervum is larger, different in shape (curved semi-cylindrical), and differently located 
in relation to the median axis of the skull; the paroccipital process also is rela- 
tively heavier and shorter, the occiput higher, and the sagittal crest more promi- 
nently developed in the latter genus. The skull which is the type of Nestoritherium 
has been crushed almost in the same manner as the skull of Moropus elatus, which 
has been described, but the two skulls show striking similarities in the breadth of 
the frontals over the orbits, their contours above, the shape and length of the 
nasals, maxillaries, and palatines. The posterior nares, however, extend further 
forward in Nestoritherium than in Moropus. 
MEASUREMENTS” oF THE CrantuM oF Moropus elatus (No. 2103, Catalog Vert. Foss., Carnegie Museum). 
Cm. 
Diameter from the occipital crest to and including P?...................... 52 
Diameter from the occipital condyle to and including P?.................... 49 
Diameter fromptheyoceipitalucondyleytowlVcseeeane eee ee eerie 28 
Diameter from the occipital condyle to anterior margin of orbit............. 30 
dransverserdiam etenolgoalatel copes ieee en rrr ee eee cee renee een 6 
diransyerse diame terol aveaie Vcr areata ree eee 8 
Greatest expansion of the zygomatic arches..................-.-0+eee+0e0: 27 
Transverse diameter at base of postglenoid processes. ...........-..02+e000- 19 
Transverse diameter at paroccipital processes...........-+-.-+---eeeeeeeee 13 
Transverse diameter of occipital condyles.................:..---+--+--+--= 10 
Venticaludiameternotoccipitalacondylesmanmee tere ernie ine 5 
Transverse diameter of frontal over the orbits..............-.+--+++-+++--e- 26 
itransyverse diameter oloccip Utara nee eErn een nenCrn ere oneGencr 13 
THe MANDIBLE. 
(Plate LIT.) 
In general outline the lower jaw of Moropus suggests that of Equus, but an 
examination of the details of structure shows marked differences between the two 
genera. The diastema between the incisors and cheek-teeth is long, as in the 
horse, and the alveolar border for the incisors is elevated to about the same degree, 
so that the incisor teeth are in a similar procumbent position; the external face 
of the horizontal ramus is, however, slightly more convex, though not nearly so 
much so, as in the tapir. The inferior border again forms a straight line as in 
Equus, but the angle has not the downward projection, nor is its lower border so 
heavy, or everted, as inthe fully adult horse. Thus the inferior and posterior 
1° These measurements are taken from the skull in its crushed condition and some may be somewhat 
greater than they would otherwise be. 
