244 Dr. R. H. Traquair on the Structure 
where this relation has been left undisturbed *. These inter- 
clavicular plates are certainly the structures which have been 
figured and described by Powrie as “ principal jugulars”—a 
mistake into which he never could have fallen had he observed 
their relation to the clavicles, or had he taken into considera- 
tion the structure of the shoulder-girdle in the recent Polypterus 
or in the extinct Paleoniscide. And in the presence and con- 
figuration of this, as of all the other elements of the shoulder- 
girdle, the closest resemblance is seen between Chetrolepis and 
the genera of fossil fishes allied to Paleoniscus, for corroboration 
of which the reader need only refer to my description of the 
same parts in Cycloptychius carbonarius}, and in Pygopterus 
(Nematoptychius) Greenockit and Amblypterus punctatust. 
Passing now to the bones of the face, we find the most 
singular conformity to the general type of structure in Palewo- 
niscus and its allies—a fact which, as already mentioned, did 
not altogether escape the notice of Pander. In the first place, 
the gape is very wide, the direction of the axis of the suspen- 
sorium and of the opereular apparatus passing obliquely down- 
wards and backwards, so as to carry the articulation of the 
lower jaw far enough behind. The superior maxillary bone 
(Pl. XVII. figs. 1&7, mx) has been very correctly figured by 
Pander, and is formed on the same type as in all the Paleo- 
niscide. It consists of a plate of bone, broad behind the eye, 
and there covering a large part of the cheek; but immediately 
behind the orbital ring the superior margin becomes suddenly 
cut out, so that the anterior extremity passes forwards below 
the orbit, tapering to a point towards the premaxillary region. 
The inferior or dental margin is not quite straight, but shows 
a slight sigmoid curve; the posterior inferior angle is rounded, 
while the short posterior margin, sloping obliquely upwards 
and forwards, joins the straight part of the superior margin 
at avery obtuse angle. Closely articulated to the maxilla 
is a rather narrow plate (fig. 7, x), consisting of two parts 
diverging at an obtuse angle. The upper and anterior of 
these les along the superior margin of the maxilla behind 
the orbit, the lower and posterior one passing down for some 
distance along the oblique posterior margin of the same bone, 
between it and the suboperculum, the centre of ossification 
* Though in the specimen represented in Plate XVII. fig. 2 the inter- 
clavicles have been forced apart, their juxtaposition is beautifully shown 
in No. 41725 of tke British-Museum collection, and many others which 
Ihave seen. They are also in contact with each other in Mr. Powrie’s 
figure ; but there both are also disjoined from their respective clavicles. 
+ Geol. Magazine, 2nd series, vol. i. June 1874. 
{ Trans. Royal Soc. Edinburgh, 1867, xxiv. pp. 707, 708. In this 
paper I called the interclavicular precoracord. 
