| 
fife of moderate size, but rather smaller than in Octodon; the lower 
jaw is larger and much stronger than in the two genera mentioned. 
In these characters the present animal makes so near an approach 
to Ctenomys, that it might with propriety be placed in that genus 
were it not that in the structure of the teeth there exists a difference 
fully as great as that which gave rise to the generic distinction of the 
little groups of which the family Octodontide is composed. In Octo- 
don, Poephagomys and Ctenomys, the enamel of the molar teeth enters, 
in the form of a fold on each side, into the body of the tooth, but the 
folds from opposite sides do not meet. In the Rodent which forms 
the subject of these observations, the crown of each molar is divided 
into two parts by the meeting of the folds of enamel of the outer and 
inner side, and the surface of these teeth may be compared to a 
series of cylinders (two to each tooth), which are much compressed 
in the antero-posterior direction. ‘The three foremost molars in 
each jaw are equal in size, and the posterior molar is smaller than 
the rest. In position, the last molar of the upper jaw differs from 
the others, being as it were twisted, so that the two transverse lobes 
are placed obliquely. 
With our present very limited knowledge of the small Rodents of 
the southern parts of South America, and especially of the western 
coast, it is impossible to judge of the value of such a modification of 
the molar teeth as is here pointed out. It is possible that the species 
of Octodontide may vary more or less among themselves in the 
structure of these teeth, in which case the so-called genera, esta- 
blished as the species are discovered, will require a revision, as do 
very many of the genera of Rodentia ; in the mean time, however, 
it is necessary that sectional names should be imposed on such 
species as will not agree tolerably well with the definitions of the 
genera published as such. Agreeably to these views, the subgeneric 
‘title Schizodon* is proposed for the present new Rodent. The prin- 
cipal external characters may be thus expressed :— 
Scuizopon Fuscus. Schiz. supra griseo-fuscus, subtis obscure flavo 
tinctus : pedibus pilis obscure fuscis tectis ; awribus mediocribus ; 
caudd, fused quoad longitudinem caput feré equante, pilis brevis- 
simis tectd. 
une. lin 
Longitudo ab apice rostri usque ad caude basin .. Sa 
as CUED So Ne 2 ad renee LeU 6 odd le DO Boat 1 8 
tarsi digitorumque .... ities, the 258 
Tit Regn (A Pek Oar aac at Ra cick eae tae cae 0 54 
In size and colouring the Schizodon greatly resembles the Com- 
mon Rat (Mus decumanus) ; its fur is rather softer than in that ani- 
smaller. It is difficult to estimate the amount of intelligence in these ani- 
mals, but, judging from the size of the brain, it would appear that there 
existed an intimate connexion between the food of the animal and its in- 
telligence ; the food in one case leading the animal to habits which cause 
it to be exposed to numerous dangers which do not occur in the other. 
* From oxifw, divido, et ddods, dens. 
