Rats allied to Oryzomys and Rhipidomys. 197 
5. [nomys, gen. nov. 
External characters as in Thomasomys; mamme not 
known. 
Skull recalling in shape that of Oxymycturus or Microxus, 
with broad low rounded brain-case and long narrow snout. 
Interorbital region smoothly rounded. Incisors small aud 
delicate. 
Molars rather narrow, their crowns higher than in any 
other of the genera now dealt with. Their foldings, how- 
ever, essentially as in Oryzomys and all the present group of 
genera, not as in Oxymycturus. 
Range. Central Peru. (Only known from Vitoc.y 
Genotype and only species. Inomys incanus, ‘Vhos. (Ory- 
zomys incunus, Vhos.). 
The distinction of this genus rests mainly on the peculiar 
shape of the skull, which, with its broad low brain-case, 
long narrow snout, rounded’ interorbital region, and small 
incisors curiously recalls that of an Ozymycturus or Microxus. 
Its molars, however, show the typical structure of the 
molars of the present group, and its interparietal is of full 
normal size. Its removal from Thomasomys renders far 
more uniform the skull-shape of the species to be referred 
to that genus, as it was the one outstanding species in this 
respect, 
The following is the description of a new subspecies of 
Delomys :— 
Delomys dorsalis collinus, subsp. n. 
General characters of true dorsalis of Rio Grande do Sul, 
the colour approximately the same, and the fur similarly 
soft and rich, and so equally differmg from the harsh-furred 
D. sublineatus of Espiritu Santo. But the size, and especially 
the size of the teeth, averages greater, the molar tooth-row 
measuring 5°0 mm. in length, while in a considerable series 
of true dorsalis this measurement is only 4°5 to 4:7 mm., 
the teeth of collinus being also perceptibly broader. No 
doubt the two forms will be found to intergrade, but the 
difference is so constant locally that it should be recognized 
by name. In the series available the belly is rather more 
whitish and less buffy, and the underside of the tail is less 
decidedly whiter than the upper than is the case in dorsalis. 
Mamme in the only female 1—2=6, instead of 2—2=8 
