PAL.EOSYOPS LEIDY, AND ITS ALLIES. 
275 
BO far as to form a true transverse crest ; thei’e are also signs of a posterior crest in this 
genus. The development of transverse crests is the great exception in this suh- 
family ; hut there are signs of these in L. laiiceps and in P. borealis. The first and 
second superior molars are always provided with two well developed internal cones 
in all the genera of this family; but the variations in the number of internal 
cones of the last xipper molar are considerable. In Limnohyops this molar has 
two internal cones, whereas in Palceosyops and TelmatotIieriu7n the hj’pocone of the 
last upper molar Ijecomes rndimentarv, although all stages of the degeneration of 
the hvpocone may be observed within the genera alreadj'^ mentioned. The Amria- 
tion in the form of the last inferior molar rvitli its tubercles Avill he considered 
later. Diastemas may he present in the dental series of some species, and the inter- 
vals increase as we approach the higher forms, although a reversion to the primitive 
form takes place in Titanotherium, which genus is Avithout a diastema in its 
dentition. 
Skull. — The general form of the skull in the two subdivisions of this family is 
A'ery diftereut. All the members of the PalcBOsyopince have small skulls compared 
Avith those of the Titanotheriince ; and, moreover, in the former the fixcial region is 
much longer in comparison Avith the cranial portion than in the latter subfamily. 
The marking off of the orbit by postorbital processes from the temporal fossa is a Avell 
marked character of Palceosyops. The coalescence of the temporal ridges to form a 
sagittal crest is characteristic of the Palceosyopinte, Avhereas in Tiianotherium no 
such crest is found, the roof of the cranium Ixeing very broad, flat and limited 
Laterally by the strongly developed temporal ridges. The nasal bones in Palt^osyops 
are more slender and elongated as compared to those of Titanotherium ; they do not 
jxroject beyond the j)remaxillary symphysis, and the lateral nasal notches are smaller 
than in the last named genus. The nasals never bear any horns, nor does any 
other part of the skull iii the Palceosyopmce. The auditory jjrocesses are large, and 
the postglenoid and posttympanic i-emain separated. In the loAver jaA\' the anterior 
extension of the symplyysis beyond the preniolars is much greater than in the Titan- 
otheriince. In the latter group the anterior portion of the syunphysis is A^ery much 
abbreA'iated and there is, consequently, a crowding together of the teeth in this 
region. The brain is less coinmluted, and the forebrain is more Avidely separated 
from the hind brain than in the Titanotheriince. 
Carpus. — In the carjxus the lunar diameters are more nearly equal than 
in Ti(anoikeriu??i, Avhere the transverse diameter of the former is much greater 
than the A'ertical. The distal fixcets of the lunar are more unequally divided, 
the lunar-magnum facet being nearly vertically placed in some genera. As 
a consequence of this the distal portion of the lunar forms a beak-like process, 
Avhich in one genus {Lininohyops) ma}' nearly diAude the second roAV of carpals 
as far as their distal face. The scaphoid and uncifonn are more displaced in 
the Paleeosyopince than in the Tilanotheriince . The articulation of metacarpal III, 
37 JOCKS. .A. S. S. PHIL.A., VOL. IX. 
