colored
sandstone. President Hitchcock has a slab showing a regular series of
tracks of this animal; the distance between the steps being about
three feet, and the tracks equidistant and alternate, which would not
be the case if the animal had been quadrupedal. In a quadruped, the
horse for example, the hind feet are set down near the fore feet, and
sometimes even strike them. Hence it must be inferred that the track
in question was that of a biped, or of a quadruped which did not use
its fore feet in progression, like a kangaroo. We naturally ask, What
kind of biped could this have been? Evidently not a man, the size of
the foot being too large to admit such a supposition; nor could it
have been a bird, the number of toes and their direction not admitting
this hypothesis.

Tetradactylous birds, or those which have four toes, have only three
of them directed forwards, and the fourth backwards, generally. There
are, however, exceptions; some birds have four toes directed forwards:
this is the fact with the Hirundo Cypselus and the Pelicanus Aquilus
of Linnaeus, or Man-of-war Bird. But the articulations are different in
the two animals, birds having regularly two, three, four, and five
phalanges, and the spur, where it exists, supported by a single
osseous phalanx; whereas the Otozoum has three phalanges in the inner
and second toe, four in the third and fourth toes. In this last
arrangement, the Otozoum is decidedly different from all known birds.
It is not likely to have been a tortoise or a lizard. The kangaroo has
four feet, and uses only two in progression, moving forward by leaps;
also, like the Otozoum, it has four toes; but the size of the toes
does not accord with that of the Otozoum, nor is the structure of the
foot the same, so far as we know. It has been suggested by Professor
Agassiz, that this animal might have been a two-footed frog. Nature
had, in those days, animal forms different from those we are
acquainted with; and this might have been the fact with the Otozoum.

* * * * *

GROUP SIXTH.

We have in this group a specimen of the track of a four-footed animal,
which may have been a frog, though different from ours. The feet are
unequal in size, and present a different number of toes. In existing
frogs there are four toes in the fore feet, and five in the hind; but,
in the specimen before us, the front toes are five in number, and the
back t