Muridze commonly referred to Akodon. 339 
Hiven after the removal of the members of Chalcomys, the 
genus Akodon tends to divide into two—the more typical 
species, light and delicate, with thinly built skulls, and gene- 
rally of a more uniform olivaceous colour, and those with 
comparatively heavy skulls, and with their colour more 
contrasted with blackish lining. The latter group seem to 
approach Zygodontomys, and may prove to intergrade with it. 
Ill, THALPoMyYS, gen. nov. 
Fur crisp. Colour of only species warm ochraceous or 
rufous. Fourth fore-claw 2°0 mim., hind 2-2. 
Skull and teeth as in Akodon, except that there is a distinct 
overhanging ledge on each edge of the interorbital region. 
Palatal foramina long, much narrowed behind. 
First molar of the only specimen available, although worn, 
showing clear trace of an anterior groove, 
Genotype. TJ. lasiotts (Mus lasiotis, Lund; LHabrothrix 
lasiotis, Winge). 
IV. THAPTOMYS, gen. nov. 
General build modified for a subterranean life, very much 
as in the most marked species of Pitymys, the tur short and 
velvety, the eyes reduced in size, and the tail shortened. 
Fore and hind claws about equal, the fourth 2-6-2°8 mm. in 
length. 
Skull strorigly built ; interorbital region very broad, with 
squared edges. Zygomatic plate scarcely projected forwards. 
Palatal foramina smallest im the group, narrow, scarcely 
reaching the level of m’. Bulle small. 
First molar with anterior notch, 
Genotype, V.subterraneus (Hesperomys subterraneus, Hens.). 
(This is probably a synonym ot “S Jdus nigrita,” Licht., but 
1 use a name about whose identification there can be no 
doubt.) 
A genus distinguished by the modifications due to a more 
completely subterranean lite. 
V. BoLomys, gen. nov. 
Fur normal or rather coarse. Colour strongly lined, with 
contrasted light underside. Claws elongated, the fore nearly 
as long as the hind; in BL. albiventer the tourth may attain 
3°3 mm. in front and 38°5 beliund. 
Skull stout and strongly built, with broad square-edged 
interorbital region. Zygomatic plate projected forward. 
