480 A FISH-EATING RAT CHAP. 
pads, a state of affairs which characterises a number of these 
Rodents. 
The genera Megalomys, Chilomys, Reithrodontomys, Eligmo- 
dontia, Nectomys, Rhipidomys, Tylomys, Holochilus, Reithrodon, 
Phyllotis, Scapteromys, Acodon, Oxymycterus, Ichthyomys, Blari- 
nomys, Notiomys are South American forms. Oryzomys and 
Lheithrodontomys are common to both parts of the New World. 
The genus J/ehthyomys is remarkable on account of its un- 
Rodent-lke habits and of certain associated structural changes. 
I. stolzmanni was obtained trom Mount Chanchamays in Peru 
at an altitude of 3000 feet; it is a habitual fish-eater, and 
lives in streams. Another species, /. hydrobates, was formerly 
referred to Habrothrix. The skull shows likenesses to that of 
the Australian Hydromys; but the most marked characters of 
adaptation are those of the teeth and caecum. The cutting 
edges of the upper incisors form a reversed V of obvious use 
in holding a slippery fish. The caecum is much reduced, short, 
and narrow. The general Otter-like shape of the creature is 
largely due to its flattened head, though its “size and general 
proportions are much as in the common Black Rat.” ' 
This sub-family contains a number of genera from Madagascar, 
viz. Brachytarsomys, Nesomys, Hallomys, Brachyuromys, Hypo- 
geomys, Gymnuromys, and Hliurus. 
Sub-Fam. 10. Neotominae.—The last sub-family of the 
Muridae is that of the Neotominae, containing the North Ameri- 
can genera Veotoma, Xenomys, Hodomys, and Nelsonia. 
Fam. 3. Bathyergidae—This family contains several genera. 
which consist of subterranean forms. All these Rodents agree 
in a number of characters, of which the principal are as 
follows :— 
The eyes are very small, and the external ears are reduced to 
the merest fringe of skin round the aural aperture. The legs are 
short, as is the tail; the hair-covering is reduced—a reduction 
which finds its culmination in the nearly nude Heterocephalus. 
Being burrowing creatures, a number of other modifications in 
accordance with this mode of lfe are to be seen in their 
structure. The upper incisors stand out in front of the closed 
lips, and prevent the entrance of earth. For the same reason 
1 See O. Thomas, ‘‘On some Mammals from Central Peru,” Proc. Zool. Soc. 
1893, p. 333. 
