EMYDA PUNCTATA. 
remarkable peculiarity is that the anterior opening of the shell is capable of 
being partly closed by the motion of the anterior pair of sternal bones, and the 
posterior opening of being completely shut by two coriaceous lobes or valves 
arising from the posterior margin of the last two bones of the sternum. 
The nuchal bone in this species is early united to the dorsal shell: it is small 
and of an oval or semilunar figure. The anterior pair of ribs are broader than 
the succeeding ones, expanding towards the margin: the posterior also are 
broad and short. The total number of ribs varies from six to nine pairs in 
the specimens which I have observed. The surface of the bone, both on the 
back and sternum, is not rugose as in many species of Trionyx , but scabrous, 
with numerous elevated round points, distributed pretty equally over the 
whole. The tail is extremely short, more so even than in Trionyx labiatus \ 
but as there is no flap of skin extending behind the margin of the bony 
shell, it still projects a little beyond the edge of the dorsum. 
There is no doubt that the habits of this animal resemble in a great measure 
those of the other species of the family, though there may probably be some 
approach to those of the Emydidoe, consonant with the marked approximation 
which we observe in its form and structure. Thus, it has not the extremely 
depressed form, and the soft, flattened and expanded margin, by which the 
Trionyx has the power of so readily concealing itself in the mud, and there¬ 
fore probably roams after its prey more in the manner of the other fluviatile 
groups. 
The structure of this animal is so interesting, as being evidently abnormal, 
that it will not perhaps be wholly unavailing to examine what are its relations 
to other groups, and to which of them it may be considered as constituting 
the annectant form. Mr. Gray has placed it at the end of the Trionychidce, 
next to Sphargis of the Cheloniadw. The characters of the latter genus, how¬ 
ever, evince a much nearer affinity to Trionyx than to Emiyda ; as the sternum 
is almost wholly cartilaginous, and the ribs are not connected with the sternum, 
and are much less extensively ossified than in any other genus. On the other 
hand, we shall discover in Emyda many important points of affinity to the 
other fresh-water groups. Passing from Trionyx, the typical form of this 
family, towards the Hydraspidce , we see in the present species a marked 
