nd turbot
belong,--were ushered into being as early as the times of the Chalk; but
the Gadidae or cod family,--that family to which the cod proper, the
haddock, the dorse, the whiting, the coal-fish, the pollock, the hake,
the torsk, and the ling belong, with many other useful and wholesome
species,--did not precede man by at least any period of time appreciable
to the geologist. No trace of the family has yet been detected in even
the Tertiary rocks.

[Illustration: Fig. 57

PTERICHTHYS OBLONGUS.

(One half nat. size.)]

Of the ganoids of the second age of vertebrate existence,--that of the
Old Red Sandstone,--some were remarkable for the strangeness of their
forms, and some for constituting links of connection which no longer
exist in nature, between the ganoid and placoid orders. The Acanth
family, which ceased with the Coal Measures, was characterized,
especially in its Old Red species, by a combination of traits common to
both orders; and among the extremer forms, in which Palaeontologists for
a time failed to detect that of the fish at all, we reckon those of the
genera Coccosteus, Pterichthys, and Cephalaspis. The more aberrant
genera, however, even while they consisted each of several species, were
comparatively short lived. The Coccosteus and Cephalaspis were
restricted to but one formation apiece; while the Pterichthys, which
appears for the first time in the lower deposits of the Old Red
Sandstone, becomes extinct at its close. On the other hand, some of the
genera that exemplified the general type of their class were extremely
long lived. The Celacanths were reproduced in many various species, from
the times of the Lower Old Red Sandstone to those of the Chalk; and the
Cestracions, which appear in the Upper Ludlow Rocks as the oldest of
fishes, continue in at least one species to exist still. It would
almost seem as if some such law influenced the destiny of genera in this
ichthyic class, as that which we find so often exemplified in our
species. The dwarf, or giant, or deformed person, is seldom a long
liver;--all the more remarkable instances of longevity have been
furnished by individuals cast in the ordinary mould and proportions of
the species. Not a few of these primordial ganoids wore, however, of the
highest rank and standing ever exemplified by their class; and we find
Agassiz boldly assigning a reason for their superiority to their
successors, important for the fact which it embodies, and wort