Plain, near Tezpur, in Assam, close to the Brahmaputra; but any way, the generic
term Chaibassia selected by Theobald is an unfortunate one.
Theobald referred this new sub-genus and Geoemyda to the family Testudi-
nidce, from which, however, their structure markedly separates them; the structure
of Geoemyda, also that of Chaibassia, being essentially that of an Emyde.
An inspection of the specimens from the Bishnath Plain in Assam, n.nrt a comparison
of them with Blyth’s types of G. tricarmata, conclusively prove that the two
are perfectly distinct species, hut generically identical.1
In 1875, I described a tortoise from Arracan, which I referred to the Genus
Geoemyda and named G. depressa.2 Mr. Theobald afterwards8 re-described the
same species under the name of Geoemyda arakcma, from specimens in the Indian
Museum, Calcutta.
I propose now to consider wherein these species of Geoemyda differ from one
another and from JEmys, to which they are closely allied, and what the characters are
of Chaibassia. I regret that I have no example of G. spinosa to compare with these
forms.
1 The animals from the Bishnath Plain are distinguished from Chaibassia tricarinata, Blyth, by the very much
larger and anteriorly broader first vertebral, the lateral margins of which are widely anteriorly divergent, the
posterior border straight and equalling one-half the breadth of the anterior border: the fourth aud fifth vertebral* are not
so large as in C. tricarinata. In the latter, the gulars are triangular, while, in the Assam species, the external lateral
margins of the gulars are rounded. The anal plates of C. tricarinata are decidedly larger than in the Bishnath species,
in which the anal notch is smaller. The form of the shells of the two species is practically the same, viz,, eloDgately
oval, relatively highly arched, downwardly shelving at the sides, and very slightly broader posteriorly than anteriorly.
The female is somewhat contracted in the Assam form at the fifth, sixth and seventh marginals, with no reversion
of the marginals, which are very feebly denticulated. A nuchal plate in both species, and three raised ridges, the vertebral
the longest, involving all the vertebral plates; the lateral ridge on the costals more feeble. The colour of the Assam shell
is black above, almost orange-yellow on the under surface ; the dorsal ridges, and the under surface and the margins
of the shell bright yellow. The head black, with a broad reddish band from above each nostril, increasing in breadth
as it passes over the eye and over the tympanum, where it ceases; a narrow similar band below the angle of the
mouth, along the inferior margin o f the lower jaw. Skin.of throat and neck pale blackish-brown, also the granulated
skin of the limbs, hind quarters and tail. Fore-limb, below the elbow, covered externally with large black scales ; a few
large black scales also behind the outer side o f the wrist; no large scales on outer surface of hind limb, except at the
onter margin of the foot, and on the hinder half of the sole; toes free; hind foot rather club-shaped; claws large
sharp and black. The colours of C. tricarinata are unknown.
The head of the Assam form is more pointed than in C. tricarinata, and the facial portion longer. These
characters are pronounced in the skull, and the frontal region is much longer and narrower than the corresponding region
in C. tricarinata, and the palatine, but more especially the pterygoid region, is distinguished from the latter by its
great breadth. The following are the measurements of the two sexes, from which it would appear, as both are adults
that the male is the smaller of the two:—
nents of C. theobaldi.
Total length of carapace
„ of plastron
Axillary breadth
breadth across back
Depth tt' rough shell
I have much pleasure in connecting Mr. Theobald’s name with this species.
2 Ann. and Mag. Nat. Hist., 4th Ser., vol. xvi, p. 284, Oct., 1875; no proof of this paper having been sent me to
correct, it is full of blunders.
3 Descr. Cat. Kept., Brit. Ind., Calcutta, 1876, Errata et add,, p. vii.
The only difference between the shells of G. grcmdis and JEmys trijuga is this,
that the shell of the former is perhaps slightly more elongated, and that each osseous
marginal plate is notched at the middle of its free border, aud the xiphiplastron
is somewhat larger than in 1Umys trijuga. The skull, while conforming to the
general characters of the posterior nares, palate, alveolar ledge of the maxilla., open
palatine foramen and broad pterygoid region of JEmys, is, at the same time, a shorter
and broader skull destitute of a quadrato-jugal, with a very broad frontal and nasal
surface.
The shell of Geoemyda depressa presents the same characters as G. grcmdis,
only, as its specific name implies, it is considerably depressed from above downwards.
The vertebral column, however, is much more flattened than in G. grcmdis, in which
the individual segments are much laterally compressed as in the small radiated land
tortoises, and JEmys in the form of its vertebrae is intermediate between G. depressa
and G. grcmdis. The skull also of G. depressa, PL lxxv figs. 1 to 5, in all its
characters is a miniature representation of the skull of G. grandi§, although it is
specifically distinguishable from it in a few of its details. There is also no difference
between the lower jaws of Geoemyda and JEmys. The bones of the feet of G. grcmdis
and of G. depressa have all the characters of the feet of JEmys, but the bones
are relatively stronger, the 5th digit of the hind foot in Geoemyda and JEmys
being provided with only one phalanx beyond the metacarpal element. The form
of the limb bones and of the carpal and tarsal constituents are the same in both,
and their respective pelves conform to one type.
The osteological differences therefore lie only in the skulls. The examination,
however, of the skulls of many examples of Emydes shows that the quadrato-jugal
bone is frequently very feebly developed, indeed so much so that it is apt to be
overlooked, and if the muscular substance is roughly removed, the bone is liable
to be detached with it. The jugal also, in some species, is reduced to a very
thin rod. In both of these species, G. grandis and in G. depressa, the jugal is not
strong, except in very old individuals.
In C. tricarmata the shell has the elongated character of G. grcmdis, but
the caudal is the only marginal element notched, and the vertebrse are broad, as
in G. depressa. The feet have much the same osteological features as in the foregoing
species, but the 3rd and 4th toes of the fore foot, but especially the 5th, are
feebler than in G. grcmdis, G. depressa, and in Emydes generally. The 5th toe of
the hind foot has the same characters as in G. grcmdis, G. depressa, and JEmys
trijuga. The pelvis and other bones agree with JEmys and with these two species of
Geoemyda.
The skulls of C. tricarmata and C. theobaldi are intermediate between the
skulls of G. grandis and G. depressa, and of such Emydes as JE. trijuga, in which the
zygomatic arch is not imperfect as stated by Gray. They have the same characters
as regards the posterior nares, alveolar ledge, flattened area between the palatine
foramina, and large palatine foramen, but the last is relatively smaller than in JEmys
trijuga. The fronto-nasal region of the skulls of C. tricarinata and C. theobaldi