PREVIOUS TO THE LAST GEOLOGICAL REVOLUTION. 55 



remind us of the true rats. The commonest species, of 

 which we shall have occasion to speak more at large hereaf- 

 ter, is distinguished from the others by a groove or furrow on 

 the front of the incisors, for which reason I propose to name 

 it Echimys sulcidens. • 



Of the genus Mus I am acquainted with five species, which 

 all appear different to those described by Azara and Reng- 

 ger from Paraguay. Two of these infest houses, the three 

 others keep out in fields and woods. One of the former ap- 

 pears to me identical with our own house-mouse [Mus mus- 

 culus), but the other is quite different from our two kinds of 

 house-rat, Mus decumanus and Mus rattus. I call it for the 

 present, Mus setosus, on account of the long black bristles 

 which are scattered here and there over its skin. This spe- 

 cies was introduced into these parts about the commencement 

 of the present century ; and it has driven out of the houses a 

 smaller species, of a pretty chocolate-brown on the back, 

 chesnut-brown on the sides, and white on the belly, with a 

 fine short fur, and a short silky tail : the latter species has 

 become rare, and is now only seen about cultivated fields. — 

 A fourth and still smaller species frequents gardens : it is of 

 the same size as our house-mouse, has a large head, with large 

 hairy ears, and a very short tail. I have named it Mus last- 

 Otis. But the most remarkable species of this genus lives 

 only in the woods. I have hitherto been unable to procure a 

 single specimen in fre§h condition ; but I have found it abun- 

 dant in the stomachs of the larger diurnal and nocturnal birds 

 of prey. Its tail is provided with stiff bristles ; on which ac- 

 count I have given it the temporary name of Mus lasiurus. 



After this cursory sketch of the rodents inhabiting this dis- 

 trict,' I shall proceed to consider them with reference to the 

 remains which they have left in the caves, in order to explain 

 thereby some points connected with the history of the fossil 

 bones in the same places. 



I commence with the common Brazilian wood-rat, Mus 

 lasiurus. I know of very few caves in which remains of this 

 animal are not found ; and in many they occur in such pro- 

 digious quantities, as to excite the utmost astonishment. To 

 convey some idea of this, I will give a brief description of the 

 first cavern of this kind that I had an opportunity of examin- 

 ing near Caxoero do Campo. Thie cavern is one hundred and 

 twenty feet long, from six to nine feet wide, and from thirty 



* The Moco (Kerodon rupestre) is not found within the district in which 

 the caves are situated, although the southern boundary of its habitat is but 

 a few degrees from that locality. 



