PALJ50SY0PS LEIDY, AND ITS ALLIES. 
325 
by a slight iiiterviil. The basioccipital is shorter and narrower than in P. paludo- 
sus and its anterior keel-like and lateral muscular rugosities are very prominent. 
The lateral vacuities of the skull are more elongated and narrower than in the larger 
species, and are encroached upon laterally by the periotic bones. The lamina of 
bone between the lateral vacuities and the foramen ovale is perfectly Hat and broad 
in this specimen. 
Sphenoidal and Pterygoid Region (PI. XI, fig. 5). — Just in front of the foramen 
ovale the roots of the pterygoid j^rocesses of the sphenoid arise, and they extend 
anteriorly to form the walls of the narrow posterior narial ojjening. The posterior 
nares in this species is much more contracted than in the Tapir. The wings of the 
sphenoid forming its inferior termination are not nearly so widely expanded as 
in the Tapir’s skull, and the whole extent of the nares from the posterior limit of 
the palate to its termination at the hamular processes, form, as it were, a narrow 
trough, the anterior and narrow walls being bent inward and thus contracting the 
narial space. The sphenoid sends wide horizontal plates posteriorly, and the ali- 
sphenoid extends about half way up the side of the temporal fossa. It articu- 
lates with the frontals and was probably shut ofi’ from articulation with the parie- 
tals as in the Tapir’s skull. The damaged condition of the specimen does not alloAv 
us to define the orbitosphenoidal region. The presphenoid is narrower and more 
elongated than in P. paludosus-, it shoAvs upon its ventral surface a prominent 
keel, and upon each side of the same are the prominent and vertical Avails of the 
alisphenoid canal. 
Squamosal . — The squamosal forms about the loAver half of the temporal fossa. 
Its external surface is not as deeply excavated as in the larger species of the genus ; 
its posterior portion presents a numl)er of small foramina. The zygomatic process 
of this species is Amry characteristic and t^uite different in form from that of P. pal- 
udosus. Instead of being bi'oad, flat and Avidely extended from the temporal fossa 
the zygoma of P. megarhinus is narrow, depi’essed and presents only a narroAV 
external face. The zygoma in this species is not set off' so far from the sui'face of 
the skidl as in others of the genus, as its extreme j)osterior joortion Avhex’e it 
joins the squamosal is narroAV. The course of , the zygomatic arch is more 
descending than in P. paludosus, and at its middle part it is thin and narroAv, being 
in this respect in strong contrast to the arch of the larger species of the genus. The 
auditory processes are peculiar in form ; the postglenoid is very short, thick and 
rugose ; the post-tympanics are also short and their surface is rough. The 
postglenoid is Avidely separated from the post-tymjxanics, so it is probable that the 
mastoid appeared upon the surface of the skull. In the skull under consideration 
there is a triangular tract betAveen the exoccipitals and post-tympanics Avhich Avas 
probably filled up by the mastoid portion of the periotic. The large venous foramen 
situated between the paroccipital and post-tympanic, Avhich is so characteristic of 
the larger species, appears to be Avanting in this skull. The glenoid facet is long 
and narrow, and the anterior surface of the postglenoid is smooth for articnlation 
with the jaw. An internal glenoid process is present in this species. 
