292 Mammatia OF INDIA. 
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 nowcome to the subdivisions of the Simplicidentata: The 
order GurrEs 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, Giinther, 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., Webetidentati, or Blunt-toothed 
Rodents, which contains only the JZesotherium, a fossil form. We have 
now to subdivide the two. The Double-toothed Rodents are easily 
disposed of in two families—ZLeforide and Lagomyide. The Simple- 
toothed Rodents are more numerous, and consist of about eighteen 
families arranged under three sections, which are Sctwromorpha, or 
Squirrel-like Rodents, JZyomorpha or Rat-like Rodents, and Aystrico- 
morpha, or Porcupine-like Rodents. It would perhaps render it clear 
to the reader were I to tabulate the differences chiefly noticeable in 
these three sections :— 
SECTION J.—ScIUROMORPHA, OR SQUIRREL-LIKE RODENTS. 
Molar dentition = or = In the latter case the foremost upper 
molar is small; the fibula is distinct, and never united, except in some 
