specimen, which consists only of the shell, and even this mutilated by the
absence of the anterior lobe of the sternum. I am therefore unable to say
anything respecting the head, limbs and tail, upon which so much depends
in ascertaining the characters of approximating species. I cannot however
avoid considering this as distinct from T. geometrica, of which Mr. Gray states
it to be a variety. The extraordinary elevation and conical form of the
vertebral plates; the minuteness of the areolae terminating the apex of the
cones; the extreme shortness of the nuchal plate; the projecting direction
of the caudal; the sternum extending backwards as far as the margin of
the dorsal shell, and the remarkable colouring of this part, are all so many
characters distinguishing it from T. geometrica, and appear to me to be
sufficiently important, taken together, to warrant the opinion which I have
adopted, that they are distinct species. It must however be acknowledged
that it would be far more satisfactory if we could examine a number of
specimens, and particularly living ones.