There are specimens, however, in which the proportion is reversed, and there are
examples with first vertebráis with straight lateral margins divergent from behind
forwards, and in these cases the shield is usually as long as broad: the posterior
margin is sinuous. The longitudinal axis of the plate is occupied by a distinct
ridge. The second, third and fourth vertebráis are nearly quadrangular and
almost of equal breadth, the first-mentioned being the narrowest. Their lateral
margins are all more or less parallel but sinuous, and the posterior margins
concave from behind forwards. The fifth forms a broad suture with the fourth,
and its lateral margins are slightly contracted in their anterior fourths, and the
length of this shield varies considerably. One marginal is in contact with the
first vertebral, four with the first costal, and three touch the second, third and
fourth; the fifth vertebral only being very narrowly in contact with the tenth
marginal. The caudals, in some specimens, project backwards slightly, as if compressed,
hut the caudal notch is absent.
The gulars project beyond the post-gulars, but are truncated in front, and their
suture exceeds that of the post-gulars. The pdstero-post-gular suture is nearly transverse
in some, but in others forms a posteriorly obtuse angle. The pectorals-
are a little longer than the abdominals, and the postero-abdominal suture is directed
backwards. The abdominals are the next longest shields equalling the post-gular
and half of the gulars, and standing in the same proportion to the preanals and anals;
The preanals are very little longer than the pectorals, and the anals equal the
pectorals and nearly one-half of the gulars. The anal notch is broad. The axillary
breadth equals one-half of the length of the sternum, and exceeds the breadth
of the sternum at the groin.
In younger females, the shell is more rounded, and in very young specimens
about 3 25 inches long, the shell is nearly round, and the first and second marginals
slightly reverted, the vertebral ridge being well developed, almost as in JPcmgshura,
forming a prominent truncated spine on the third vertebral and all but absent
on the fifth shield. The sternal ridge is strongly marked. The gulars nearly
equal the post-gulars in length; the pectorals, the abdominals, and the preanals
equal nearly the anals; the two last pairs of shields being only a little longer
than the first.
On carefully examining about 100 living examples of this species, I found that,
there were two distinct forms of shell, one a large, full and globose shell, and the other
a more depressed and more elongated oval; the animals of the former characterized
by short tails, and those of the latter with long tails, but that with these exceptions
the animals of the two forms of shell were identical. On dissecting a number of
examples of each type, it was found that the deep and shortly oval shells with the
short-tailed animals were females, and the longer ovals and more depressed shells
with long-tailed animals were males.
The adult male is a narrower and more elongated oval than the female and
considerably smaller, measuring 6 inches in a straight line. I t differs also in
form by the less arched character of the shell, both antero-posteriorly and transversely.
I t has also the anterior margin of the shell slightly reverted and the caudal
region more produced downwards. The dorsal ridge is also more marked. The
interval between the margin of the carapace and the sternum is less than in the
female, and instead of being convex, as in the latter, it is irregularly flat and concave,
the sterna! ridge being much more developed than in the opposite sex, and the
sternum slightly contracted at its middle and always more or less concave, with the
margins tending to reversion. The anal notch is also deeper than in the female.
The plates of the carapace and sternum ,are much the same as in the female, and
they are very thin in both sexes, and are very easily rubbed off.
Shells o f B . (M.) ocellata, D. & B.
1 9 5 9 9
Length of carapace in a straight line . . . . . r . .
Breadth between second and third costals over curve . . . . .
Length of sternum in straight l i n e ................................................. .........
Axillary breadth . . . . . . . .
Inguinal » ,, • • • . . . . . . . . .
Depth through third v e r t e b r a l ........................................................... ..........
6-1* 6-2
5-2
2-7
2-5
5-11 6-1
4-10*
2-4*
2-4
8-5
9-2
7-4
3-6
3-10
4-1
8-2
8-6
7-1
3-5
3-5*
3-8*
In males, measuring as above, the carapace is wholly ossified, while in females of
the same size there is a considerable unossified area between all the costals and marginals,
which would appear to be conclusive proof of the smaller size of the male.
The snout is short and rather pointed, and the nostrils close together, round,
and directed forwards. The margins of the jaw are finely serrated, and there is
a notch in the front of the upper jaw, with a tooth on either side of it between
which the symphysial hook of the lower jaw is received. The upper surface of the
head is flat, and covered by one plate; and there is a large plate behind the eye. The
plate of the mandible is backwardly convex on the chin, and there is a sma.ll plate
below its extremities and below the angle of the mouth. A series of very small scales
behind the angle of the mouth; the mental glands each open by two orifices in the
usual position. Skin of tympanum nearly smooth. Neck moderately long; the
skin on its upper surface nearly smooth, with scattered minute round blackish
papillae; the skin on the sides and under surface somewhat scaly and papillar. The
base of the neck is smooth, as is also the skin on the groin. The fore feet are broad
and powerful; the toes broad, and the five claws strong. The toes are covered- with
from five to six transverse plates, and the upper surface of the free portion of the
limb with separate transverse plates. The sole is covered with rounded plates, above
which there is a transverse naked area, succeeded by a transverse row of three
large plates. The outer margin is fringed with five to six largish plates. The upper
surface is nearly free of transverse scales, except on the sides, and there are a few
scattered minute papillse on the bare portions. The tail is short, but it projects
one-half of its length beyond the carapace. The latter half of its under surface
has a double row of enlarged scales. Its sides and upper surface are covered with
sharp conical tubercles, among which some larger ones occur on the sides.