is the
ARGOZOUM DISPARIDIGITATUM. It is leptodactylous, and remarkable for
the length of the middle toe. We have another species, which is
smaller than the last named, and in which the toes are nearly of equal
length; hence called ARGOZOUM PARIDIGITATUM.

The other genus of this group is the PLATYPTERNA, and our specimen
is named _Deaniana_. This genus is remarkable for the width of the
heel; hence the name, from _platys_, _broad_, and _pterna_, _a heel_.
It has three toes like the other genera of this group.

* * * * *

GROUP THIRD.

This and the succeeding group are tetradactylous; having one toe
behind, three forwards.

The third group is leptodactylous; foot usually small, but sometimes
of medium size. Of it we have two specimens, viz.: ORNITHOPUS
GALLINACEUS, and ORNITHOPUS GRACILIS. The former is so called from the
resemblance to the domestic fowl: for convenience sake, in this and
other instances, we use the whole for a part. It is about three inches
in length, and the Ornithopus Gracilis about two.

This latter specimen is particularly interesting. It consists of two
parts, which open like the covers of a book. These covers present four
impressions: first, the superficial, which is distinct, slender, and
beautiful--the heel is broad; second, corresponding with this
depression and on the inside, is a figure in relief as distinct as the
depression; third, on the inside of the second cover is a depression
corresponding with the relief last mentioned; fourth, on the outer
side is a second relief corresponding with the second depression, but
less distinct than either of the other three, still, however,
exhibiting three toes pointing anteriorly, but the hind toe is
wanting. The whole of this double slab forms a series of cameos and
intaglios, measuring four inches by three, and in thickness an inch
and a quarter.

* * * * *

GROUP FOURTH.

Of the fourth group we have five specimens. The _Triaenopus_, so called
from its resemblance to a trident, has besides three leptodactylous
toes pointing forwards, a fourth extending backwards in a remarkable
way, like the handle of a trident; the impression, however, being
expanded so as to show an extensive displacement of the mud. All the
specimens of Triaenopus are in a beautiful red shale, very thin and
fragile, but presenting well-defined impressio