PALiEOSYOPS LEIDY, AND ITS ALLIES. 
upon sup)erior molar 3 which is wanting in that of F. validus, although, strange to 
say, in the latter species this tooth is provided on one side with a well developed 
nietaconule. In T. cultridens the internal basal cinguhnn of the premolars isstrongl\' 
developed and complete. I regard this completion of the internal cingula of the 
premolars as heing a higher dental character than the incomplete cingula. T. 
hyognat/ms is the highest species of the genus and is the transition form iK-tween 
Telmatothemmi mxA Diplacodon, as will be shown later when I consider tlie evo- 
lution of the lower jaw. 
The Skull. — The skull presents a great variety of form in this subfamily, and 
in some species a great development of the occipital crests with an elongation of the 
cranio-facial axis is the rule, while in other species the skull is shorter, with a 
tremendous convex development of the frontal region. Owing to the lack of 
material 1 am totally unable, unfortunately, to give an idea of the form of the 
skull in a number of species. Fimnohyops laticeps has the most primitive form of 
skull. In this species, as we have already seen, the cranium is greatly drawn out, 
producing an extremely long cranial region and a short facial portion. The orbits 
are small and placed veil over the alveolar border of the jaw. 'I'lie occipital ci-ests 
are more strong^ developed than in any othei- species of the subfamily'. I'he iut»T- 
orbital region is hollowed out and cnhnmates in narrow and elongatetl na.sal.x. In 
the form of its nasals and strong zygomatic arches P. /m’dfr;«aj)proaches L. laticeps 
more nearly than any other species. The palate in all the species of this siihfainily 
is short and never extends beyond the second superior molar. The |)rinlitive char- 
acter of the premaxillaries of L. laticeps is shown in their short ami roiind form. It 
is interesting to note that the contour of the skull of L. laticeps mon* clo.sely 
approaches that of Titanotherium than any other species of thi‘ Palceosyopiuir. 
Palceosyops megarhinus apx)ears to have a low grade of skull, its form iH-ing 
elongated and much depressed. The orbits are small and placed far 
forward. The premaxillary and nasal regions are highly specialized, and tliller con- 
siderably from those of the moi'e primitive type of skull seen in P. paludosus. 'flic 
characters of the zygomatic arch and malar insertion ot P. megarhinus dilliu' viny 
much from those oi P . paludosus and L. laticeps. The broad shelf-like malar of I\ 
megarhinus is unique in character. 
The form of the skull of/’, paludosus is somewhat specialize<l and is hardly in 
conformity^ with the low tyqie of its dentition. As Ave see, the marktul excavation ol 
the anterior frontal region and its great bnlbiform enlargemenl distinguish 
it from other allied species of the genus. The facial region is considerably 
elongated and the temporal fossa shorter and higher than in L. laticeps. 
P. paludosus agrees with all the other species of this lamily in not having tla* orbit 
separated from the temporal fossa, constituting a primitive chaiuuder pei-sisting in 
all the members of this subfamily. The premaxillaries of P. paludosus i-etain the same 
primitive form as in Limnohyops. The nasals, on the contrary, an* shorter and 
broader than in the latter genus. In all the above mentioned species the auditory 
