in
the ganoidal and placoidal orders. The period of these orders seems to
have been nearly correspondent with the reign, in the vegetable kingdom,
of the Acrogens and Gymnogens, with the intermediate classes, their
allies. At length, during the ages of the Chalk, the Cycloids and
Ctenoids were ushered in, and were gradually developed in creation until
the human period, in which they seem to have reached their culminating
point, and now many times exceed in number and importance all other
fishes. We do not see a sturgeon (our British representative of the
ganoids) once in a twelvemonth; and though the skate and dog-fish (our
representatives of the placoids) are greatly less rare, their number
bears but a small proportion to that of the fishes belonging to the two
prevailing orders, of which thousands of boat-loads are landed on our
coasts every day.

The all but entire disappearance of the ganoids from creation is surely
a curious and not unsuggestive circumstance. In the human family there
are races that have long since reached their culminating point, and are
now either fast disappearing or have already disappeared. The Aztecs of
Central America, or the Copts of the valley of the Nile, are but the
inconsiderable fragments of once mighty nations, memorials of whose
greatness live in the vast sepulchral mounds of the far West, or in the
temples of Thebes or Luxor, or the pyramids of Gizah. But in the rivers
of these very countries,--in the Polypterus of the Nile, or the
Lepidosteus of the Mississippi,--we are presented with the few surviving
fragments of a dynasty compared with which that of Egypt or of Central
America occupied but an exceedingly small portion of either space or
time. The dynasty of the ganoids was at one time coextensive with every
river, lake, and sea, and endured during the unreckoned _eons_ which
extended from the times of the Lower Old Red Sandstone until those of
the Chalk. I may here mention, that as there are orders of plants, such
as the Rosaceae and the Grasses, that scarce preceded man in their
appearance, so there are families of fishes that seem peculiarly to
belong to the human period. Of these, there is a family very familiar on
our coasts, and which, though it furnishes none of our higher ichthyic
luxuries, is remarkable for the numbers of the human family which it
provides with a wholesome and palatable food. The delicate Salmonidae
and the Pleuronectidae,--families to which the salmon a