STRUCTURE AND AFFINITIES OF THE PLATYSOMID. 367 
pterygoid is connected a distinct guadrate (qu, figs. 2 and 10) projecting down- 
wards to articulate with the lower jaw ; above which, and extending also along 
the upper margin of the pterygoid, whose posterior projecting wing it overlaps 
internally, is another plate (m.pt. figs. 2 and 10) of a triangular form, broad 
behind and narrowing to an acute angle in front, which seems to be the 
equivalent of the mesopterygoid of other fishes. The obvious resemblance which 
the palato-quadrate apparatus bears to that of the Paleeoniscidée will be noticed 
further on.* 
The mandible is stout and deep, and as regards its constituent elements 
three may be easily recognised,—the dentary, splenial, and angular; the arti- 
cular was doubtless also present, but isnot well defined. The dentary (d, fig 1, 
9, and 10) carries, however, no teeth, its upper margin forming a thin sharp 
edge ; its anterior extremity is pointed, prominent, and excavated above, so as 
to resemble the preemaxillary beak opposed to it. Behind it on the outer sur- 
face of the posterior extremity of the jaw is a well-marked angular (ag, figs. 
1 and 10) resembling that of the Palzoniscide. The splenial element (sp, figs. 
6, 7, 8 and 10), covering the inner as well as folding over the upper aspect of the 
Meckelian cartilage, has its oral surface provided with a patch of enamelled 
‘tubercles similar to those of the palate. Its upper margin shows two ridges 
coalescing posteriorly, and of these the external one is the most prominent, and 
becomes anteriorly gently convex in its contour, while the other, proceeding in 
a straight direction, gets lower down as it passes forwards. The inner ridge 
is also set with a few sharpish dental tubercles, which, however, vary much in 
prominence in different individuals; they are not found at all in the original of 
“M‘Coy’s C. pes-rane, but I fear that this circumstance can hardly be con- 
sidered as constituting a specific mark, as in many specimens of C. granulosus 
from North Staffordshire they are nearly entirely obsolete. 
The contour of the mazilla (figs. 4 and 5, mz fig. 1) is almost identical with 
that of the same bone in Lurynotus, but its lower margin is thin and sharp, 
like the corresponding one of the mandibular dentary element, and shows not 
the slightest trace of teeth of any kind. But on its internal aspect (fig. 4), and 
just above the edentulous margin, there is a narrow band of small thickly-set 
flattened and enamelled tubercles, resembling those which we have found to 
occur in patches upon the inner surface of the pterygoid and splenial bones ; 
this band curving suddenly downwards towards the margin at the junction of 
the posterior and middle thirds of the bone. The premazille (p.mz, fig. 1) 
are, as Professor Youne has described them, a pair of triangular beak-like 
bones, whose oral edges are sharp but edentulous. 
* Here it is, however, necessary to note that I was formerly inclined to consider the bone, which in 
the Palzoniscid head corresponds to that which I have above referred to the mesopterygoid element, to 
be metapterygoid in its nature (Carboniferous Ganoid Fishes, pt. i. Pal. Soc. 1877, p. 18.) 
VOL, XXIX. PART I. 5B 
