while the tail establishes this creature among the vertebrata and the
fishes, its mouth has been opened vertically, like those of the
crustaceans, but which is contrary to the mode of vertebrata
generally. This seems a pretty strong mark of the link character of
the coccosteus between these two great departments of the animal
kingdom. The pterichthys has also strong bony plates over its body,
arranged much like those of a tortoise, and has a long tail; but its
most remarkable feature, and that which has suggested its name, is a
pair of long and narrow wing-like appendages attached to the
shoulders, which the creature is supposed to have erected for its
defence when attacked by an enemy.

The holoptychius is of a flat oval form, furnished with fins, and
ending in a long tail; the whole body covered with strong plates
which overlap each other, and the head forming only a slight rounded
projection from the general figure. The specimens in the lower beds
are not above the size of a flounder; but in the higher strata, to
judge by the size of the scales or plates which have been found, the
creature attained a comparatively monstrous size.

The other fishes of the system,--the osteolepis, glyptolepis,
dipterus, &c., are, in general outline, much like fishes still
existing, but their organization has, nevertheless, some striking
peculiarities. They have been entirely covered with bony scales or
plates, enamelled externally; their spines are tipped with bone, and,
as one striking and unvarying feature, the tail is only finned on the
lower side. The internal skeleton, of which no traces have been
preserved, is presumed to have been cartilaginous. They therefore
unite the character of cartilaginous fishes with a character peculiar
to themselves, and in which we see pretty clear vestiges of the pre-