Tetraonyx affinis, Cantor, Journ. As. Soc., Bengal, vol. xv, 1847, p. 612 {pars),
Tetraonyx basJca¡ Duméril, Cat, Méth. Bep., p. 15, 1851,
Clemmys longicollis, Strauch, Chelon. Stud., 1862, p. 88; id. Vertheil. der Schildkr. 1865 p. 87.
Snout pointed and turned upwards, the upper surface concave between the
anterior half of the orbits, convex behind this. The facial portion is much more
pointed, up-turned and narrower than in B. Imeata, and the nostrils are more
tubular. An elongated shield between the orbit and the anterior upper half of the
tympanum, with a very narrow elongated shield below it and the aural border.
Tympanum covered with rather small scales, arranged somewhat in concentric
circles. The skin granular on the neck and on other parts of the body as in
B. Imeata^ with similarly defined scales. The jaw is feebly serrated and slightly
notched anteriorly.
The general colour of the upper surface of the head and neck in the female is
olive-green, with the homy covering of the jaws yellow, the under surface of the neck
being also more yellow than the upper surface; the limbs and tail being dark olive-
green. The claws yellow. The upper surface of the shell is a uniform olive-brown,
the under surface yellow.
The shell has no ridge in adult lifej hut the young has a rather pronounced
vertebral ridge. The shell is not so elongately oval as in B. Imeata and is more
expandecWposteriorly and has more reverted marginals. I t is also generally more
arched from side to side in its anterior half; broader before and m*Uch fuller over the
region of the first and second vertebráis and first costáis, than in the generality of
shells of B . Imeata. I t attains its greatest depth between the second and third
vertebráis. I t is distinguished from B. lineata by the more quadrangular form
of its vertebráis, but more especially by the absence of the fourth elongated vertebral
of that species.
The nuchal is not so broad posteriorly as in specimens of the same size of
B. Imeata. Like that species, the first vertebral has divergent lateral margins, but
the hinder margin, if it is at all concave, is not so much so as in B, Imeata, and it
is occasionally quite straight. I t is broader than long, its greatest breadth being
between the costo-marginal angles, and its posterior breadth also either exceeds or
equals the length. The shield is marked by a feeble longitudinal swelling. The
second vertebral is also broader than long. Its first costal margin is directed backwards
and outwards and is nearly straight, the second costal border being directed
inwards and backwards from the former, with a sinuous outline. The posterior
border is very faintly concave from behind forwards. The greatest breadth of the
shield is attained between the two costáis, the breadth of the posterior border
scarcely equalling the length of the shield. The third vertebral is also a little
broader than long, and only slightly broader in its anterior than in its posterior
margin which is backwardly concave. Its greatest breadth is attained between the
second and third costáis, and if its slight outward projection at that point is
omitted, the two sides of the third plate are nearly parallel, but a little posteriorly
convergent. The fourth is considerably broader than long, and the front margin
broader than the hinder suture. The third costal sutures are sinuous and posteriorly
divergent, while the fourth costal margins are the reverse, and nearly straight. The
second and third vertebráis are nearly of equal breadth, and the fourth is only a
little narrower than the last. The fifth is much broader than long, with a straight
truncated anterior margin, half as broad as its posterior margin. The caudal notch
is hardly perceptible.
The guiar suture is shorter than in B. Uneata, equalling about one-third or one-
fourth of the post-gular suture. The latter almost equals the pectoral suture, which
is less than the two former sutures by about one-half of the guiar suture. Thé
abdominal is the longest suture, but the preanal suture is shorter than the conjoint
guiar sutures. The anal suture is less than the greatest breadth of one of its shields.
I have not observed any very great disproportion between the males and
females of this species, but the largest specimen that has passed under my observation
was a female from Kyouk Phyoo on the coast of Arracan, which greatly exceeded
the dimensions of any male, but still not to that degree that seems to prevail
in B. tJmrgi, B. cfovomcelli and some other species.
The only structural difference that I can detect between the two sexes, is the
much greater length of the tail in the male, as compared with the female, which
is brought out in the accompanying table :
Measurements o f shells o f B. baska, Gray.
1575 16-75
13-75 15-00
500 5-75
5-25 5-75
6-25 675
14*50 16-20
7-50 4-90
Length of carapace, straight line
„ of plastron
Axillary breadth ,
Inguinal „ ■ ... -.. I
Greatest depth o f shell ,
Breadth of shell over curve, greatest
Length of caudal vertebrae
In adolescence, the nasal portion of the skull of the male is perhaps more
pointed and upturned than in the female at the same period. In youth, however,
the skull of the male is alinost flat (see PI. lxxv4 figs. 6 to 10) as is shown
in a specimen from the Irawady which has all the skull characters of this species, and
regarding the specific identity of which there can he no doubt. Unless the specific
characters of the adult are well ascertained, the young of such species as B. baska
and of other species of Batagw, owing to the great changes in form that take place
between youth and age in the shell characters, are very liable to he mistaken for
distinct species. I may also add that unless the characters which distinguish the
sexes are well known, similar errors are liable to arise regarding them, and, moreover,
the sexes can only he satisfactorily determined by a direct appeal to the organs of
generation.
The male, however, is distinguishable from the female by the remarkably
brilliant colouring of the front part of the body, hut this is not always present, and
may perhaps depend on sexual periods.