The Bridger beds have yielded a great abundance and variety
of land, marsh, and fresh-water chelonians. They present much
variation of form and size; and, owing to the great pressure in the
strata, scarcely any two specimens of the same species are alike;
occasionally, however, an undistorted specimen is obtained.
The most abundant remains of turtles are those of a species of the
recent genus _Emys_, which are found in all the beds, and are,
perhaps, the commonest fossils of the basin. The genera _Trionyx_ and
_Hadrianus_ (_Testudo_, Leidy) follow next in order.
HADRIANUS, Cope.
Resembles _Testudo_ in form, but has two analscuta, as have most
_Emydidæ_.
Hadrianus allabiatus, Cope.
U. S. Geol. Survey of Territories, 1872, p. 630.
Represented by two ungual phalanges which resemble the claws of
_Testudo_, but are proportionately shorter, broader, and not so
pointed at the ends. They are oval in section, both longitudinally
and transversely; the articular faces are deep and subinferior.
From Henry's Fork.
Hadrianus octonarius, Cope.
Geol. Survey of Terrs., 1872. p 630.
Represented by the right humerus of a large individual.
This bone is intermediate in character between the corresponding
bones of _Testudo_ and _Emys_. The head is longer and narrower than
in the former genus; it is implanted on a short, distinct neck,
and is strongly convex in both directions. The articular surface
extends to the base of the internal tuberosity. The tuberosities,
especially the external one, are very large and thick. The external
rises above the head, and resembles that of _Emys_ in shape. The
fossa separating the tuberosities is comparatively narrow. The shaft
is much like that of _Emys_, but is somewhat more strongly curved;
not so much, however, as in _Testudo_, and the distal end is not so
much flattened. The anconeal fossa is wider and deeper than in either
genus. The trochlea is broad, and divided by an obscure groove into a
small and convex radial face, and a nearly plane (transversely) ulnar
face. The condyles are prominent and rugose.
Found near Dry Creek.