28 
NOKTH GALLEHY. 
[UTPISU 
The order is commenced in Wall Case No. 1, by the Cephalaspides, 
a family peculiar to the Devonian period. The species of which it is 
composed were fishes in which the body was protected by large bony 
plates, was convex above, and flat beneath ; the pectoral fins were 
represented by large bony appendages, situated close behind the head ; 
and the tail was tolerably long, tapering, and furnished with small 
scales. The second family of the order, the Ccelacanthi, so called 
from the spines of their fins being hollow, occupy the compartments 
3 to 5 of the same Wall Case. In the 6th compartment are arranged 
the Dipterines, including fishes of the Old Red Sandstone and Coal 
formations, having the body protected by rhomboidal scales, and pro- 
vided with two back fins, as well as two anal fins. The specimens 
exhibited are chiefly from Scotland. In the 7th compartment are 
arranged the Acanthodians. The fishes of this family are characterized 
by the minuteness of their scales and having each fin armed with a 
strong bony spine. They are mostly from the Devonian of Scotland. 
The family of the Sauroids (see compartments 8 to 12), contains 
fishes which exhibit both the uneven-lobed and the even-lobed structure 
of tail, and is divided accordingly into two minor groups : the Sauroids 
have conical teeth mixed with minute prickly teeth. The scales vary 
considerably in form. This family presents living examples in the Bony 
Pikes {Lepidosteus) of the rivers and lakes of North America, and in 
the Bichirs (Polypterus) of the Nile. The Sauroid family is represented 
by numerous extinct species ranging through nearly all geological 
strata down to the Devonian. 
The Ganoid family called " Lepidoids " (see compartments 13 to 21) 
have the same rhomboidal scales as the Bony Pikes, but in general 
form they are shorter and have a greater vertical diameter ; the teeth 
are of one kind only, and of a more or less conical form. 
The last family of the fishes with ganoid scales is the Pycnodonts, 
of which all the principal genera will be found in compartments 21 
and 22. Like the members of the preceding group, these fishes have 
a short, high, and compressed form. Their teeth are usually large, 
rounded, and with low crowns admirably fitted for crushing shell-fish. 
Many of the species are from the Jurassic (or Oolitic) rocks ; some are 
from the Chalk, and a few extend into the Tertiary formations, but 
there are no known living species. 
In the preceding two great divisions of Fishes many of the families 
of which they are composed are extinct, and a very large proportion of 
the species is confined to the geological strata beneath the Chalk, 
whilst those which now come under consideration belong entirely to 
the Glial k and Tertiary formations, and the families have living re- 
presentatives. They form two important sections — the Ctenoids and 
the Cycloids. The Ctenoids, which are distinguished by their scales 
being serrated, or finely notched at the free edge, are arranged in 
compartments 23 to 26 : the common Perch is a good example of this 
group. The Cycloids occupy the compartments 27 to 36. Their 
scales have the edges smooth. The Fishes of the Mackerel tribe 
[Scomberida), of the Carp tribe (Cyprinida), of the Pikes (Esocidce), 
