48o A FISH-EATING RAT 



pads, a state of affairs which characterises a number of these 

 Eodents. 



Tlie genera Megalomys, Chilomys, Heithrodontomys, Migmo- 

 dontia, Nectomys, MJiipidomys, Tylomys, Holochilus, Reithrodon, 

 Phyllotis, Scapteromys, Acodon, Oxymycterus, IcMTiyomys, Blari- 

 nomys, Notiomys are South American forms. Oryzomys and 

 Bheitlirodontoynys are common to both parts of the New World. 



The genus Ichthyomys is remarkable on account of its un- 

 Eodent-like habits and of certain associated structural changes. 

 /. stolzmanni was obtained from Mount Chanchamays in Peru 

 at an altitude of 3000 feet ; it is a habitual iish-eater, and 

 lives in streams. Another species, I. liydrolndes, was formerly 

 referred to Hahrothrix. 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, Brcwliyuromys, Hypo- 

 geomys, Gyrnnuromys, and Eliurus. 



Sub-Fam. 10. Neotominae. — The last sub -family of the 

 Muridae is that of the Neotominae, containing the North Ameri- 

 can genera Keotoma, Xenumys, Hodcnitys, and Kelsonia. 



Fam. 3. Bathyergidae. — This family contains several genera 

 which consist of subterranean forms. All these Eodents 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 life 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 



' See O. Thomas, "On some Mammals from Central Peru," Proc. Zool. Soc. 

 1893, p. 333. 



