858 Messrs. Hancock & Atthey on Reptile- and Fish-Remains 
worn away. It is, however, generally persistent towards the 
outer margin of the plate; a little further back it is almost 
invariably removed; and still further back, on the older por- 
tion of the plate, the peripheral wall of hard matter is scarcely 
ever found, having undoubtedly been worn down by the action 
of the jaws. It is therefore clear enough that, in accordance 
with the line of the section, we might have the margins of 
the tooth-like processes rough, without any distinct peripheral 
wall; as in the figure of the so-called teeth of Saganodus; or 
there might be such a wall, without any external enamel; or, 
again, both the enamel and peripheral wall might be present : 
and such a series of sections of Ctenodus we possess. Were 
we, then, ignorant that the sections were made from different 
parts of the same object, we might readily be led to erect 
three distinct genera on the palatal plate of a single species of 
Ctenodus. And, again, were we disposed to create species, 
various degrees in the obliquity of the section would afford 
excellent opportunities for so doing, as the tooth-like processes 
would vary in length and form in each section. 
Paleoniscus Egertoni, Agassiz. 
Two large patches of scales, representing the greater portion 
of the fish, have occurred at Newsham. ‘The scales are in a 
very good state, and show the characteristic markings of this 
very pretty species; when examined with the microscope, it 
is perceived that the surface of enamel is regularly covered 
with extremely minute punctures or dots. The larger patch 
is one inch and five-eighths long, and upwards of three-eighths 
of an inch wide. The fins are not displayed; neither are there 
any traces of head or tail. 
Several other Palwonisci have been found in our shales, as 
well as one or two species of Amblypterus. ‘There is also in 
the collection a specimen or two of what we take to be a spe- 
cies of Hurylepis, Newberry. Though these are not in a very 
perfect condition, they are in a much better state of preserva- 
tion than the specimens of P. Egertont. In many of them the 
head is present; and both the tail and fins are frequently de- 
terminable. Several of them are probably new; but at pre- 
sent we cannot enter more fully on this branch of the subject, 
and must leave it for some future opportunity. A few words, 
however, may be said on the dentition of these fishes, particu- 
larly as it seems to be little understood; indeed it appears 
that little or no attention has been given to this matter. 
M. Agassiz, in his great work, ‘ Poissons Fossiles,’ states 
that the teeth of Palewoniscus are “ en brosse”’ (tome 1. pt. 1. 
p-42); but the words which immediately precede this expression 
