MIDDLE OLD RED SANDSTONE. 
445 
If we except the Placoids already alluded to, and a few 
other families of doubtful affinities, all the Old Red Sand¬ 
stone fishes are Ganoids, an order so named by Agassiz from 
the shining outer surface of their scales; but Prof. Huxley 
has also called our attention to the fact that, while a few 
of the primary and the great majority of the secondary 
Ganoids resemble the living bony pike, Lepidosteus^ or the 
Amia^ genera now found in North American rivers, and one 
of them, Lepidosteus^ extending as far south as Guatemala, 
the Crossopterygii, or fringe-finned Ich thy elites, of the Old 
Red are closely related to the African Polypterus^ which is 
represented by five or six species now inhabiting the Nile 
and the rivers of Senegal. These North American and Afri¬ 
can Ganoids are quite exceptional in the living creation ; 
they are entirely confined to the northern hemisphere, un¬ 
less some species of Polyptems range to the south of the line 
in Africa ; and, out of about 9000 living species of fish known 
to M. Gunther, and of which more than 6000 are now pre¬ 
served in the British Museum, they probably constitute no 
more than nine. 
If many circumstances favor the theory of the fresh-water 
origin of the Old Red Sandstone, this view of its nature is 
not a little confirmed by our finding that it is in Lake Supe¬ 
rior and the other inland 
Canadian seas of fresh wa¬ 
ter, and in the Mississippi 
and African rivers, that we 
at present find those fish 
which have the nearest af¬ 
finity to the fossil forms of 
this ancient formation. 
Among the anomalous 
forms of Old Red fishes 
not referable to Huxley’s 
Crossopterygii is the Pte- 
rlchthys^ of which five spe¬ 
cies have been found in the 
middle division of the Old 
Red of Scotland. Some 
writprd hnvp pnTminvprl Agassiz; Upper side, showing 
W1 liers nave corapai ea month ; as restored by H. Miller. 
their shelly covering to 
that of Crustaceans, with which, however, they have no real 
affinity. The wing-like appendages, whence the genus is 
named, were first supposed by Hugh Miller to be paddles, 
like those of the turtle; and there can now be no doubt that 
they do really correspond with the pectoral fins. 
