242 
PROFESSOR H. G. SEELEY ON THE STRUCTURE, ORGANIZATION, 
palato-nares. The lateral excavation shows the palatine plate to extend upward and 
inward as in other specimens. 
The distorted condition of the specimen makes detailed measurement of little 
value. The head is about 13 centims. long, and the height of the vertical face is 
about 8'5 centims. from the cutting margin of the jaw to the flattened frontal region. 
The circular nares are rather above the middle of this height; each is 2 centims. in 
diameter, and the bar which divides them, formed by the nasal bones above and the 
pre-maxillary bone below, is half a centim. wide. The pre-maxillary bone is extremely 
narrow (about 2 centims.), and may be divided by a median suture, though the state 
of preservation does not demonstrate this point, and the appearance may be delusive. 
The circular orbit is 4 centims. in diameter; the malar bone extends internally to the 
post-frontal at its hinder border, and both bones are overlapped externally by the 
squamosal, which at once rises to a level with the crown of the head as it extends 
backward. At the back of the head is a slender sigmoid bone, expanded at both ends, 
about 9’5 centims. long, which may be the clavicle. 
These characters anq^ly establish the distinctness of this species, and make its 
reference to a distinct genus not improbable; but I do not regard the vertical opposi¬ 
tion of the pre-maxillary and mandible on which Lystrosaurus was founded as a 
suflicient definition of the genus. 
The Skull of Hyorhynchus platyceps, Seeley. (Plate 15, figs. 1-3.) 
A skull, which is imperfect both in front and behind, registered in the British 
Museum as R. 872, received from Mr. Thomas Bain, is so remarkable in its form that 
I regard it as probably indicafing a new genus. It is characterized by a slender 
angular Pig-like snout, relatively large orbits, and a narrow parietal region. 
The upper surface of the head is flattened, slightly convex from front to back in the 
median line, with the superior borders of the orbits somewhat elevated, so as to make 
the frontal bones between them longitudinally concave. The post-orbital region has a 
length of 3 centims. as preserved, and is about 12 millims. wide at the posterior 
fracture, where a transverse section shoivs that it is the summit of a vertically ovate 
region of the brain-case. As in so many other allied forms, its lateral walls diverge 
outward as they extend forward to the posterior angle of the orbit, where the post¬ 
frontal bone extemls transversely outward. The post-frontal is very slender. It is 
directed at first outward and downward, and then downward and forward, making the 
posterior boundary of the orbit. This aperture on each side of the head looks outward 
and a little upward, is 4 centims. long, by 3'3 centims. deep. The wfidth of each 
frontal bone from the median suture to the orbital border is 1‘6 centim. in the middle of 
the orbit. The sutures are badly defined. The parietal appears to be overlapped 
by the post-parietal bone, which extends forward to the post-frontal, and has the side 
flattened and oliliquely inclined. At about 1'5 centim, behind the orbits is the long 
