388 DR TRAQUAIR ON THE STRUCTURE AND AFFINITIES 
mandibular element, articulates behind with the operculum and suboperculum, 
and externally with the great “pre-opercular” cheek plate along the narrow 
eroove, already described, on the hinder edge of the inner aspect of that bone. 
Lastly, by the anterior two-thirds of its outer margin, it is immovably fixed to 
the maxilla, and then recedes a little inwards from that bone before passing back 
to the quadrate articulation, so that, as already mentioned, an interval is left 
posteriorly for the passage of the masticatory muscles. In spite of the most 
careful examination, I have not been able to discover the lines of demarcation 
between the probable constituent elements of this apparatus, which in its general 
relations, though considerably broader in form, corresponds closely with that in 
the recent Polypterus. 
The /ower jaw (Mn) is long, and, though pretty robust, is more slender than 
in the Saurodipterini; near the front, its lower margin is slightly excavated. 
Seen from the side it is tolerably straight; from below it is, as we might expect, 
gently curved inwards towards the symphysis. Not much can be made out 
regarding its component elements, though the dentary is evidently powerfully 
developed, and a small narrow detached plate (fig. 5) lying on one of the slabs 
near a head, and having on one margin a few minute conical teeth, is in all pro- 
bability the splenial. 
The space between the two mandibular rami, on the under surface of the 
head, is occupied by two very narrow jugular plates (7), each of which is acutely 
pointed in front; there is no trace either of an azygos jugular, or of lateral ones. 
Dentition—The dentition of Jvristichopterus is clearly enough exhibited in 
several of the specimens. The lower jaw of one shows two stout sharp conical 
teeth, each measuring + inch in length by a little more than , inch in diameter 
at the base; they are both so split that the external surface is seen only towards 
their apices. Another specimen exhibits three mandibular teeth of nearly the 
same dimensions, and entire except at their bases, besides one maxillary tooth 
with its apex broken off, and the complete impression of another. A detached 
tooth, quite entire (Pl. X XXII. fig. 8, magnified), found in the same bed with 
the other remains, and from its shape and markings undoubtedly belonging to 
the same species, measures nearly 33; inch in length by +4 in diameter at the 
base. Besides these larger teeth, the presence of smaller ones, some being very 
minute, is obvious; some of these are seen on the premaxillary of the head 
represented in fig. 1. All these teeth are of an acutely conical form, slightly 
incurved, and very sharp; their external surface is brilliantly polished, but not 
smooth in every sense, being closely fretted all over with very minute and short 
longitudinal indentations, passing, indeed, into fine strice at the base. A distinct 
fluting is also observed at the bases of the larger teeth. 
In the detached palato-quadrate arch represented in fig. 3, a portion of the 
upper jaw has remained attached to its outer margin, showing the bases of some 

