188 HISTORICAL PALAEONTOLOGY. 
apparently disappeared; and the principal types of the Car- 
boniferous belong to the groups respectively represented at 
the present day by the Gar-pike (Lefidosteus) of the North 
American lakes, and the Polypterus of the rivers of Africa. Of 
the former, the genera Pa/goniscus and Amblypterus (fig. 130), 
Ty 
Ki 
ate Cry me 
I im Aenea, cy \\ 
Fi 
— 
g. 130.—A weblypterus macropterus. Carboniferous. 
with their small rhomboidal and enamelled scales, and their 
strongly unsymmetrical tails, are perhaps the most abundant. 
Of the latter, the most important are species belonging to 
the genera Megalichthys and Rhizodus, comprising large fishes, 
with rhomboidal scales, unsymmetrical (‘ heterocercal”) tails, 
and powerful conical teeth. ‘These fishes are sometimes said 
to be *‘ sauroid,” from their presenting some Reptilian features 
in their organisation, and they must have been the scourges 
of the Carboniferous seas. The remains of //acoid fishes in 
the Carboniferous strata are very numerous, but consist wholly 
of teeth and fin-spines, referable to forms more or less closely 
allied to our existing Port Jackson Sharks, Dog-fishes, and 
Rays. The'teeth are of very various shapes and sizes,—some 
with sharp, cutting edges (Petalodus, Cladodus, &c.) ; others in 
the form of broad crushing plates, adapted, like the teeth of the 
existing Port Jackson Shark (Cestracion Philippi), for breaking 
down the hard shells of Molluscs and Crustaceans. Amongst 
the many kinds of these latter, the teeth of Psammodus and 
Cochliodus (fig. 131) may be mentioned as specially charac- 
teristic. The fin-spines are mostly similar to those so common 
in the Devonian deposits, consisting of hollow defensive spines 
implanted in front of the pectoral or other fins, usually slightly 
curved, often superficially ribbed or sculptured, and not un- 
commonly serrated or toothed. The genera Crenacanthus, 
Gyracanthus, Homacanthus, &c., have been founded for the 
reception of these defensive weapons, some of which indicate 
fishes of great size and predaceous habits. 
