56 
THE EACES OF THE MASCARENES. 
this species is the extraordinary width of the anterior and posterior openings, the 
sternum being very short, with both lobes contracted. 
The normal shape of the carapace of the young (Plate XXII.) is a regular oval with 
subvertical sides, a moderate declivity in front, and a strong declivous expansion behind. 
No part of the margin is visibly reverted ; and the vertebral plates are scarcely raised in 
their central portion. There is no nuchal plate ; and the gular and broad caudal were 
undivided. 
In two out of the four normal specimens the sternum is slightly concave, in the two 
others nearly flat. The anterior lobe is broader than long, truncated in front, or more 
or less tapering. The posterior is still shorter, with a very broad subtruncate or 
somewhat rounded hinder margin. 
With regard to the fifth specimen (Plate XXL), we may assume as almost certain 
that it was of the male sex, and rather more advanced in age than the others. The 
front portion of the dorsal shield is unfortunately broken] away and lost; but the 
perfectly level central profile of the three middle vertebral scutes shows clearly that 
there was no declivity of the outline in front ; and the lateral margins of the front 
opening appear to have been somewhat reverted. The hind portion of the dorsal cara- 
pace is much produced backwards ; and its marginal plates are expanded in a quite 
remarkable manner, being almost horizontal. The anterior portion of the sternum is 
much constricted, tapering in front, with concave lateral margins. Posterior lobe short 
and truncated as in the other specimens. The postgular plates approach so close to the 
abdominals that the intervening portion of the pectorals is reduced to a narrow strip. 
The following are the principal measurements of three of the specimens : — 
Leugth of 
carapace. 
Width of 
carapace. 
Sternum. 
Caudal plate. 
Instr. liue. 
Over curve. 
In str. line. Over curve. 
Length. 
Width. 
Length. Widtl 
Spec. 
in. 
ill. 
in. 
in. 
in. 
in. 
in. in. 
? 
161 
201 
10 
22 
11 
9 
If 4 
? 
16 
19 
20 
11 
8| 
li 4 
6 
21 (?j 
24(?) 
IH 
201 
15 
101 
1| 4| 
Cervical vertehrw. — All the cervical vertebrse are of a comparatively slight build, with 
thin walls for the spinal canal, with simple and low crests, and with the articular 
processes but slightly diverging. 
Of the majority a considerable number of specimens have been collected ; and we 
have sufficient means of judging of the amount of variation in each vertebra, also of 
comparing it with the corresponding bone in the other allied species ; but, unfortu- 
nately, we do not possess a perfect series of the vertebrse of one and the same individual ; 
and although some more or less perfect series may be selected as apparently belonging 
to the same individual, such connexion between them is by no means a matter of 
absolute certainty : yet it would have been of some importance to obtain correct data as 
