102 WHITEAVES ON FOSSIL FISHES FROM 
plate, shewn in Pander’s restoration, which is copied in Prof. Owen’s “ Palæontology.” 
On each side, too, between the postlateral (No. 9) and the marginal (No. 7, the “os angu- 
lare” of Pander) a small and longitudinally narrow plate (No. 9a) seems to be intercalated, 
though this may possibly be part of the postlateral. 
Superior or “orbital” opening situated nearly in the centre of the cranial shield, 
transversely elongated, about twice as broad as long, rounded and a little expanded at 
both ends and concavely and shallowly constricted in the middle, both above and below. 
In the centre of this opening, but on a lower level than-that of the plates which surround 
it, there is a plate (No. 6) which is evidently homologous with the “median” plate of 
Owen and the “os dubium” of Pander. It is somewhat quadrangular in outline, broader 
than long and broadest behind ; its front and side margins are concavely emarginate and 
its posterior angles appear to be produced into narrow and pointed processes which 
curve outward. But the space on each side of this median plate is nearly filled up by 
what appears to be a small, broadly oval plate (No. 6a), whose larger axis is nearly at a 
right angle to that of the whole “orbital” opening. Between the median plate (No 6) 
and the premedian (No. 4), there is a small and transversely elongated plate (No. 60) of 
the shape indicated in the diagram. A specimen, in which the front of the head happens 
to be broken off in a line with the upper margin of the “orbital ” opening, shews that the 
central portion of the front of the little plate, 6b (of which an enlarged outline is given 
on the right hand side of the diagram of the upper surface in Plate VI), is continued 
downward, at nearly a right angle, as a narrow linear process (d) less than a millimetre 
in breadth and about four mm. in length; after which it widens, at a right angle to the 
longer axis of the body, into a small and narrowly pentangular expansion about two mm. 
broad and three in length, which reaches nearly as far as the inner surface of the anterior 
ventral plates, though these are very much crushed upwards. The deflected portion of 
this little plate (d) is somewhat similar to part of the hyoid apparatus of Clarias as figured 
by Prof. Huxley,! but its outer surface appears to be enamelled and sculptured like that 
of the dermal plates of the head and trunk, which would hardly be the case if the bones 
of which it is composed were exclusively internal. 
On each of the abruptly deflected lateral margins of the cranium, outside of the 
postmarginals (No. 7), the marginals (No. 3), and the lateral terminals (No. 2a), and in a line 
with the shoulders of the pectorals, there are two side plates, one in front of the other 
the anterior of which (A) is very small, and the posterior (B) comparatively large, though 
rather narrow. The smaller one (A) is distinctly articulated to plate 2a as well as to 
plate B, while the larger one (B) is as distinctly articulated to plates 3 and 7 of the 
cranial shield and to the upturned and recurved edge of the ventrolateral (No. 19), as well 
as to plate A. The small and more darkly shaded area marked C, at the cuter and poster- 
ior angle of side-plate B, on each of the lateral margins, in each case represents that 
portion of the ventrolateral which is bent up from below. 
The posterior margin of the cranial shield is reflected inward in such a way as to 
form an articulating surface of attachment to the dorsal body shield. The exact contour 
and other details of this articulating surface, which is exposed only in a rear view of a 
single specimen of a detached cranial shield, are represented by Fig. 3 of Plate VI. 


1 Memoirs of the Geological Survey of the United Kingdom. Figures and Descriptions illustrative of British 
Organic Remains. Decade x. p. 35. fig. 21. 

