246 Dr. R. H. Traquair on the Structure 
They were figured and described by Powrie, who considered 
them, however, to be “lateral jugular plates’-—an opinion 
which, I think, he would scarcely have advocated save as 
a corollary to his view that the imterclavicular plates were 
“principal” jugulars. The branchiostegal rays are beautifully 
displayed in a specimen in Lord Enniskillen’s collection 
(Pl. XVII. fig. 1), in no. 41725 of the British-Museum col- 
lection, and also in nos. 134 and 360 of the Hugh- Miller col- 
lection. ‘Twelve of them are counted below each mandibular 
ramus in Lord Enniskillen’s specimen, though there may 
have been more; and of these the anterior one on each side 
is large, broad, and somewhat triangular in shape, the rest 
bemg long and narrow. In a specimen of Amblypterus punc- 
tatus, Agass., from Wardie, now before me, and of which I 
have given a diagrammatic sketch in a paper already quoted, 
exactly the same arrangement of branchiostegal rays or plates 
is seen, with this exception—that between the two large an- 
terior ones a lozenge-shaped azygos one is placed immediately 
behind the symphysis of the jaw; but of this I have never 
seen any very clear evidence in Chetrolepis. 
There is very distinct evidence in Chevrolepis of a circle of 
plates surrounding the orbit, asin Paleoniscus, but concerning 
which it is impossible to furnish any more special details ; 
Pander indeed mentions the arrangement as being formed by 
one large perforated plate. 
Specimen no. 41310 of the British-Museum collection shows 
that the top of the head was traversed longitudinally by a pair 
ot slime-canals followimg a flexuous course, similar to those 
in Paleoniscus ; but I have never seen any specimen showing 
the individual bones of the cranial roof so well as to enable 
one to make a satisfactory figure of them. What I have been 
able to observe confirms Pander’s statement as to the two 
parvetals, followed by a pair of more elongated frontals. 
External to these there seem to lie on each side two plates, the 
posterior of which would seem to represent the squamous plate 
seen outside the parietal in Lepidosteus and Amia, while the 
anterior may correspond to the postfrontal scale-bone seen in 
the last-mentioned fish. These have nothing to do with the 
three bones mentioned by Pander as occupying a similar 
position, and marked 46, x and y, in his figures, which, 
as he himself surmises, undoubtedly belong to the shoulder- 
eirdle and face. The snout seems to have been rounded and 
blunt ; but no specimen which I have seen has revealed any 
thing describable regarding the bones of the nasal region, in- 
cluding the premaxilla. The same must unfortunately be 
also said of the side walls and base of the skull, of the 
