Th<: ILad of Di7iichthys. — Claypole. 203 
the supra-occipital and is in turn overlapped by the marginal (of 
Newb. and Traq.). In front it is overlapped by the concave edge 
of the parietal. It may be noted that this plate does not extend 
so far forward as was represented by Dr. Newberry. The space 
thus set free is taken up by the parietal. 
(3.) The MargiiKil (N. and T.) forms the outer and hinder 
margin of the head running to a blunt point at its termination. 
As said above it overlaps the ex-occipital. It also overlaps the 
parietal inwardly and underlaps the post-orbital in front. It is a 
massive plate folding inward and downward as shown in the figure 
(see section) so as to form part of the roof of the mouth and at 
the same time to serve as the front wall .of a deep fossa receiv- 
ing the insertion of the muscle whose function was to lift the 
mandible (temporo-masseter). The hinder margin of this fossa 
is formed by the ridge of the supra-occipital mentioned above. 
These characters can be seen more or less plainly in the two 
figures above quoted (Monog. iv and Lii) but can be more dis- 
tinctly comprehended from the plan and sections given herewith. 
(4.) The Pit.rletal plate occupies a post-median position in the 
skull and is large and important. Meeting on the median line for 
a short distance its fellow of the opposite side, its edge inclines 
backward and outward overlapping largely' the supra-occipital and 
ex-occipital behind. It is in turn overlapped by the marginal 
and post-orbital and again overlaps the frontal. It is thick and 
heav}', projecting far on the inner face of the skull and forming 
the front wall of the fossa already mentioned. It appears to have 
been the solidifying element of the mid-skull, extending as a 
ridge from the marginal to the supra-occipital on the inner face. 
Judging from the conventional form which he has given to this 
plate in his restoration, its outlines cannot have been clearly de- 
fined in the specimen which Dr. Newberry studied. Instead of 
the small and elliptical area which he has assigned to it, it has a 
large size and an irregular outline and the insertion of this plate 
as above described makes a considerable ditference in the post- 
median region of the skull. 
(5.) The Frontal plate, as the parietal, meets its fellow along 
the mid-line for an inch or more and forms but a very small part 
of the outer face, being largely concealed by the adjoining plates 
all of which it underlaps. These are the parietal, supra-occipital, 
pre-orbital, post-orl)ital and ethmoid. It is a thin plate wiiich 
