he error of confounding the remains of two distinctly
different animals.

Might I beg leave to add, for the information of your correspondent, that
no British naturalist "of any mark or likelihood," has ever assumed that
(though undoubtedly sloths) either the _Mylodon_, _Scelidotherium_, or
_Megatherium_, were climbers. Indeed, the whole osseous structure of those
animals proves that they were formed to uprend the trees that gave them
sustenance. By no other hypothesis can we intelligibly account for the
immense expanse of pelvis, the great bulk of hind-legs, the solid tail, the
massive anterior limbs furnished with such powerful claws, and the
extraordinary large spinal chord--all these the characteristic features of
the _Mylodon_.

Whether there were palms or not at the period of the telluric formation, I
cannot undertake to say; but as A FOREIGN SURGEON assumes that a palm is an
exogenous tree (!), I am induced to suspect that his acquaintance with
geology may be equally as limited as his knowledge of botany. Besides, what
can he mean by speaking of a sloth "the size of a large bear?" Why, the
_Mylodon_ must have been larger than a rhinoceros or hippopotamus. The
veriest tyro in natural history would see that at the first glance of the
massive skeleton.

It is a painful and ungracious task to have to pen these observations,
especially, too, in the case of a stranger. But "N. & Q." must not be made
a channel for erroneous statements, and we "natives and to the manner born"
must be allowed to know best what is in our own museums.

W. PINKERTON.

Ham.

* * * * *

PHOTOGRAPHIC CORRESPONDENCE.

_Stereoscopic Angles._--Like many of your correspondents, I have been an
inquirer on the subject of stereoscopic angles, which seems to be still a
problem for solution. What is this problem? for until that be known, we
cannot hope for a solution. I would ask, is it this?--_Stereoscopic
pictures should create in the mind precisely such a conception as the two
eyes would if viewing the object represented by the stereograph._ If this
be the problem (and I cannot conceive otherwise), its solution is simple
enough, as it consists in placing the cameras _invariably_ 2-1/2 inches
apart, on a line parallel to the building, or a plane passing through such
a figure as a statue, &c. In this mode of treatment we should have two
pictures possessing like stereosity with those on the retinas, and
consequen