Chap. XL] 
OLD EED FOSSIL FISHES. 
263 
the northern seas of Devonian age, and the sediments therein accumulated, 
must be considered to have specially favoured the life of certain Fishes, 
whose remains are not to be detected when we pass into more southern 
tracts, where such conditions no longer prevailed. 
In the central zone of Caithness and Orkney, and its diminished equiva- 
lents in Cromarty, Nairn, Elgin, and Banff, are found many species of the 
following genera of Agassiz, viz. Pterichthys, Coccosteus,Cheiracanthus, 
Diplacanthus, Cheirolepis, Dipterus, Osteolepis, Diplopterus, and Platygna- 
thus *. 
Two of the most peculiar of these forms, Pterichthys (including Pam- 
phractus) and Coccosteus, when first found, appeared so unlike Fishes that 
all the skill of Agassiz was required to refer them to that class. 
Coccosteus decipiens, which is here represented, was first put together 
with consummate talent by Hugh Miller, from several of its detached 
fragments which that ingenious philosopher collected on the shore of Cro- 
marty. 
The other genera above mentioned have more obvious piscine cha- 
racters. These characters are apparent even in fragments of those fossils 
which were first published by Sedgwick and myself from the flagstones of 
Caithness, — such, for example, as Dipterus and Osteolepis, first described 
by Cuvier at my own request. Another of these Fishes is here represented. 
Fossils (71). Ganoid Fish op the Old Red Sandstone. 
Dipterus macrolepidotus, Ag., of the black schists of Caithness. From a specimen in 
the cabinet of Sir Philip de M. Grey Egerton, Bart. 
•This figure of a specimen in Sir P. Egerton's cabinet is more correct 
than that given in my first edition. The extra anal fin supposed to exist 
in this genus and some allied forms is not seen in this specimen, which 
shows the ordinary arrangement of a pair of pectoral and a pair of ven- 
tral fins, with a single anal fin in advance of the great caudal appendage. 
Such, no doubt, is the true structure of Dipterus and Diplopterus, which 
were predaceous Ganoids of the Sauroid family. Their forms, though of 
great breadth in proportion to their depth (something like that of the 
Gurnard of our coasts), were compact and graceful. 
The breadth and depression of the head in these fishes is well seen in 
* These Caithness Fishes were first noticed in and myself, Trans. G-eol. Soc, 2nd ser„ vol, iii. 
1826, in my memoir on the Coal of Brora in p. 142, pis. 15, 16, 17. They were partially de- 
Sutherlandshire, Trans. G-eol. Soc., n. s., vol. ii. scribed and named by Cuvier, who compared them 
p. 314 ; and were afterwards placed in their proper with the Lepidosteus, 
geological position, in 1827, by Professor Sedgwick 
