374 Messrs. Hancock & Atthey on Reptile- and Fish-Remains 
These sharp prolongations are merely the ridges or keels de- 
scribed above as extending from the apices downwards, seen 
still projecting after their base (the dentinal support) has been 
removed. ‘The same appearance is presented at the apex of 
the figure of Aganodus undatus, and strengthens our opinion 
of the nature of that form. ee 
At the point of the largest spine of Ochlodus there is evi- 
dence of two of those ridges or keels, one probably being a 
lateral ridge, the other apparently the intermediate or dorsal 
one. At the extremity of the small lateral spine, one of the 
strong lateral keels is well exhibited; and the small central 
spine displays distinct evidence of two keels. In many of our 
sections these ridges assume the very same appearance which 
we see in this figure; and they are all found to be composed 
of enamel, as these points are represented to be in Ochlodus 
and there can be no fiona that the trace of enamel described 
and indicated at g, on the large spine, is a lateral view of the 
keel the lower point of which terminates at g. 
We thus find that Ochlodus does not only agree in general 
form, but even in the minutest details, with Diplodus ; and we 
can find no distinguishing histological characters on which to 
found this so-called genus. 
Ctenoptychius pectinatus, Agassiz. 
This species is not uncommon in the shales at Newsham 
and Cramlington. One of the authors of this paper has a 
large suite of specimens gathered at these localities; they: 
agree perfectly well with C. pectinatus, though they usually 
have a greater number of denticles than represented in the 
figure in ‘ Poissons Fossiles.’ The number ranges from 
eight or nine to fifteen or sixteen. Well developed specimens 
measure one-quarter of an inch wide and a little less high. 
They are in the form of wide, flattened plates, with the ya 
margin a little arched transversely and denticulated, the den- 
ticles being rather obtusely pointed, compressed from before 
backwards, and recurved; the marginal surface is concave 
behind and convex in front, and thickened posteriorly, where 
it is strongly defined from the base by a deep transverse con- 
striction. A lateral section consequently presents a sigmoid 
curve, the lower member of which is the larger and less bent. 
The whole of the denticulated margin, including the denticles, 
is coated with a thin layer of enamel, only traces of which can 
usually be seen in sections. The base narrows suddenly im- 
mediately below the denticulated margin, and is frequently 
considerably longer than the upper glazed or enamelled por- 
