4 
MUSEUM BULLETIN NO. 12. 
the foremost part of which constitutes the hinder border of the 
orbital opening. In advance of its midlength, in line with the 
centre of the horn-base the bone is much reduced in breadth 
by the upper curve of the orbital opening externally, and by 
an emargination of its border (postfrontal fontanelle) internally. 
The breadth of the bone is here occupied almost entirely by the 
base of the horn-core which externally curved down into the orbit. 
From its inner side the edge of the bone runs obliquely forward 
and outward close under the steep inner anterior face of the horn- 
base. Anteriorly the bone curves concavely forward as a narrow 
spur to meet the nasal. Antero-extemally it extends outward 
conspicuously as the upper front part of the orbital rim acting 
as a buttress to the horn-base, and no doubt in life serving as a 
protection to the eye. Elsewhere, above and behind, the rim 
of the orbital opening rounds into the surrounding bone without 
any protrusion. 
The postfrontal ends postero-laterally beneath in a rather 
straight suture which underlaps the jugal. This suture reaches 
the orbital rim low down in the orbit. Behind, the suture 
for the squamosal passes upward onto the upper surface in the 
form of a deep groove into which the edge of the squamosal 
fits. At its upper end this groove enlarges into a pit or socket 
for the reception of a forwardly directed peg from the squamosal. 
Posteriorly the bone apparently reached the edge of the supra- 
temporal fossa between the squamosal and the median portion 
of the neck-frill as in Styracosaurus, Centrosaurus, and Chas- 
mosaurus. Its inner edge forms a concave curve cutting into 
the slope descending from the horn-base. This edge is the lateral 
boundary of the postfrontal fontanelle in advance of the suture 
between the postfrontal and the anterior end of the median 
frill element (coossified parietals) so clearly preserved in the type 
of Styracosaurus. In front the line of contact with the pre- 
frontal runs outward and forward and then obliquely inward 
to the nasal with which latter element the postfrontal was in 
sutural contact for a short distance at right angles to the longi- 
tudinal axis of the skull. 
The prefrontal (Plate IX, figure 1) is irregularly five sided. 
Its upper surface is somewhat concave sloping slightly downward 
