still remains in the form of original papers, and is
not yet embodied in text-books. They are quite as interesting, as
curious, and as diversified as those of the Jurassic epoch, which are,
however, much more extensively known, on account of the large
collections of these animals belonging to the British Museum. It will be
more easy to understand the structural relations of the latter, and
their true position in the Animal Kingdom, when those which preceded
them are better understood. One of the most remarkable and numerous of
these Triassic Reptiles seems to have been an animal resembling, in the
form of the head, and in the two articulating surfaces at the juncture
of the head with the backbone, the Frogs and Salamanders, though its
teeth are like those of a Crocodile. As yet nothing has been found of
these animals except the head,--neither the backbone nor the limbs; so
that little is known of their general structure.

[Illustration: Fig. 1. An Ichthyosaurus.]

The Ichthyosauri (Figure 1) must have been very large, seven or eight
feet being the ordinary length, while specimens measuring from twenty to
thirty feet are not uncommon. The large head is pointed, like that of
the Porpoise; the jaws contain a number of conical teeth, of reptilian
form and character; the eyeball was very large, as may be seen by the
socket, and it was supported by pieces of bone, such as we find now only
in the eyes of birds of prey and in the bony fishes. The ribs begin at
the neck and continue to the tail, and there is no distinction between
head and neck, as in most Reptiles, but a continuous outline, as in
Fishes. They had four limbs, not divided into fingers, but forming mere
paddles. Yet fingers seem to be hinted at in these paddles, though not
developed, for the bones are in parallel rows, as if to mark what might
be such a division. The back-bones are short, but very high, and the
surfaces of articulation are hollow, conical cavities, as in Fishes,
instead of ball-and-socket joints, as in Reptiles. The ribs are more
complicated than in Vertebrates generally: they consist of several
pieces, and the breast-bone is formed of a number of bones, making
together quite an intricate bony net-work. There is only one living
animal, the Crocodile, characterized by this peculiar structure of the
breast-bone. The Ichthyosaurus is, indeed, one of the most remarkable of
the synthetic types: by the shape of its head one would associate it
with the