han two incisors, coated only in front
with enamel are termed SIMPLICIDENTATA, or _Simple-toothed Rodents_.
The other sub-order, the genera of which have rudimentary incisors,
as in the case of hares, rabbits, &c., and in which the enamel is
spread more or less over all the surface, is termed DUPLICIDENTATA
or _Double-toothed Rodents_, and this is the system I propose to
follow.

SUB-ORDER SIMPLICIDENTATA.
SIMPLE-TOOTHED RODENTS.

These, as I before observed, are those of the order which never have
more than two incisors in the upper jaw, and the enamel on these is
restricted to the front of the tooth. They have also a well-developed
bony palate, which in the Duplicidentata is imperfect, forming in
fact but a narrow bridge from one jaw to the other. In the latter
also the fibula, which is anchylosed to the end of the tibia,
articulates with the calcaneum or heel-bone, which is not the case
with the simple-toothed rodents.

We now come to the subdivisions of the Simplicidentata. The order
GLIRES has always been a puzzling one to naturalists, from the
immense variety of forms, with their intricate affinities, and there
is not much help to be gained from extinct forms, for such as have
been found are mostly referable to existing families. The
classification which I have adopted is, as I said before, that
elaborated by Mr. E. R. Alston, F.G.S., F.Z.S., and reported in the
'Proceedings' of the Zoological Society for 1876. I said that he had
founded it on Professor Gervais' scheme, but I see that the
groundwork of the system was laid down in 1839 by Mr. G. R. Waterhouse,
then curator of the Zoological Society, and it was afterwards, in
1848, taken up by Professor Gervais, and subsequently added to by
Professor Brandt in 1855, and Lilljeborg in 1866. About ten years
later Mr. Alston, working on the data supplied by the above, and also
by Milne-Edwards, Gray, Gunther, Leidy, Coues, and Dr. Peters,
produced a complete system of classification, which seems to be all
that is to be desired.

We have already divided the rodents into two sub-orders, to which,
however, Mr. Alston adds a third, viz., _Hebetidentati_, or
Blunt-toothed Rodents, which contains only the _Mesotherium_, a
fossil form. We have now to subdivide the two. The Double-toothed
Rodents are easily disposed of in two families--_Leporidae_ and
_Lagomyidae_. The Simple-toothed Rodents are more numerous, and
consist of about eighteen families arranged under thre