FISHES OF THE CARBONIFEROUS SYSTEM. 107 
course, that the stream of time flowed steadily on through the geological 
ages; and we have reason to believe that over vast areas of the earth’s sur- 
face constant marine conditions have prevailed, and there the stream of life 
flowed on without break, and the geological record must be without chap- 
ters or sections. But from time to time the sea overflowed its banks, and 
left landmarks which form convenient division lines of history. Such an 
event occurred at the close of the Hamilton age and the beginning of the 
Chemung. It seems to me more natural, therefore, to consider the latter 
the introduction of a new age, the Carboniferous. In regard to the Catskill 
there is less difference of opinion, and it is now quite generally referred to 
the Carboniferous age. 
The first notice of the remains of fishes in the Catskill group was 
published by Prof. James Hall.’ In this paper are figured the scales of a 
species of Holoptychius, considered identical with H. nobilissimus, Ag., from 
the Scotch Old Red Sandstone. It is, however, a distinct though closely 
allied species, the scales of the American fish being not more than half the 
size of the Scotch, and having smoother and more continuous enameled 
ridges than those of the type specimen. 
Later (1856) Prof Joseph Leidy described* a number of fish remains 
from the Catskill of northern Pennsylvania, among others the scales and 
part of a cranial plate of this fish, to which he gave the name of Holoptychius 
Americanus. Some conical teeth having striated bases and a circular section 
were also referred to Holoptychius, but the relationship is uncertain, inasmuch 
as they were not found in connection, and it is quite possible that the teeth 
belong to some other one of the several Ganoid fishes associated with Holop- 
tychius in the Catskill rocks. Professor Leidy also referred to Holoptychius 
a scale or plate,‘ of which the exterior surface is covered with tubercles 
arranged in flexuous and confused lines. This we now know is not a scale, 
properly speaking, but a dermal plate of a different fish, which has left 
abundant remains in the Catskill, and which I have considered a species of 
Bothriolepis. 
\Nat. Hist. New York, pt. 4, Geology, 1843, p. 280, wood cut 130, figs. 1, 2, 3. 
2 Mon. des Poissons Fossiles, etc. (Old Red Sandstone), pl. 23. 
3 Jour. Acad. Nat. Sci., Phila., 2d series, vol. 3, p. 163. 
4Ibid., pl. 17, fig. 4. 
