Rats allied to Oryzomys and Rhipidomys. 193 
plate little projected forward. Palatal foramina short and 
little open. Posterior palate of the general structure of 
that of Oryzomys and Cicomys, not as in Rhipidomys and 
Thomasomys. 
Upper incisors approaching the vertical, angle with tooth- 
row abont 80°, deep antero-posteriorly, their front surface 
flattened and inclined inwards, so that the resulting relations 
of the two teeth and the shapes of their tips are about as 
in the Dormice, not as in any of the genera above mentioned. 
Lower incisors of corresponding form, anteriorly, their roots 
extended backwards much beyond the normal, forming a 
prominent capsule outside the jaw, halfway between the 
coronoid and the condyle. Both the shape and implant- 
ation of the incisors therefore indicate unusual gnawing 
powers. 
Molars showing a remarkable modification of the structure 
found in Gicomys and Oryzomys, for while the number 
and positions of the cusps are the same, the various foldings 
and ridges between and connecting the cusps are almost 
entirely obsolete. The teeth are therefore almost as in 
certain Phyllostomid bats, with smooth glossy surface and 
simple conical cusps, which are evenly spaced, slightly 
slanted backwards, 6, 4, and 2 in number on the three 
teeth. Below the teeth are similarly modified, the cusps 
slanting forwards. 
Genotype. Khagomys rufescens (Hesperomys rufescens, 
Thos.). 
Without a much greater knowledge than I possess of the 
structural modifications of the molars of this group, and the 
systematic value that should be attached to their simpli- 
fication in Rhagomys, I should not venture to express a 
definite opinion as to its affinities, but I should suppose it 
to be, on the whole, most nearly allied to Gcomys, with 
which it agrees in general facies and palatal structure, but 
from which, as from every other genus of the group, it may 
be readily distinguished by the remarkable modification of 
both incisors and molars above described. 
Still younger specimens of Rhagomys will be very welcome 
to show what trace of the normial foldings and ridges is 
exhibited by the molars when absolutely unworn; but it 
is evident there cannot be much. 
Of the second group, those with the mesopterygoid fossa 
continued forward between the posterior molars (Rhipidomys, 
Thomasomys, &c.), the doubtful species are more numerous, 
and I find the whole group needs revision, owing to the 
