366 RAMSAY H. TRAQUAIR ON THE 
with great distinctness. There are two parietals (p) in contact with each other 
in the middle line, in advance of which are two somewhat longer frontals (/). 
External to each parietal and the posterior part of the outer margin of the 
corresponding frontal is a large squamosal (sq), in front of which there is a 
smaller posterior frontal (p./), forming the posterior-superior part of the orbital 
margin. The anterior-superior part of the orbital boundary is formed by another 
plate, the anterior frontal (a./), which articulates both with the frontal and pos- 
terior frontal, and seems to pass down towards the preemaxilla; but I have not 
obtained a satisfactory view of the median superethmoidal, which was probably 
intercalated between the two anterior frontals, nor of the nasal openings, 
although it is unlikely that these parts differed much from what we have found 
in Mesolepis. The base of the cranium displays a powerfully-developed para- 
sphenoid, but I have not yet seen any specimen in which ossification in the 
lateral walls could be determined. 
The hyomandibular (fig. 10, h.m) is an elongated bone, whose direction is 
from above downwards and slightly forwards. Above it shows a large 
flattened “head,” articulated to the side of the cranium below the squamosal; 
below this head the bone is much constricted, and then assuming a cylindrical 
form, it gradually expands again in diameter towards its inferior termination, 
which is situated somewhat above and behind the quadrate articulation. There 
is no evidence of any symplectic. 
A powerful palato-quadrate apparatus (Plate V. figs. 2 and 10) extends 
forwards from the front of the lower part of the hyomandibular towards the 
snout. In my previous paper on the skull of Chetrodus (Amphicentrum), I was 
inclined to consider this as consisting of one piece, though I likewise stated 
that it was not certainly so, and that I had observed what seemed to me to be 
traces of a separate ossification towards its posterior-superior angle. Sub- 
sequent investigation has confirmed the latter view of the case, and has 
brought to light the existence of three elements,—quadrate, pterygoid, and 
mesopterygoid. The pterygoid or palato-pterygoid (pt. figs. 2, 3, and 10), 
which is the largest, has a “body” of an elliptical shape, pointed at both ends, 
and having on this flat lamina or wing (y, fig. 3) projecting upwards along 
the posterior part of its upper margin. Its outer surface is concave, its inner 
or oral surface is gently convex, and bears a patch of tolerably prominent shin- 
ing tubercles, some round, some oval, by which the roof of the mouth is rough- 
ened and armed. Its lower margin is convex, and presents two prominent 
ridges, separated by a groove, but coalescing behind in an acutely V-shaped 
fashion; each of these ridges, the external of which is more prominent than the 
other, is armed with a single row of small tuberculo-conical tooth-like projec- — 
tions, rather distantly placed, and varying much in number and degree of 
prominence in different individuals. With the posterior extremity of the 
