168 The Rev. E. J. Bunnow's Description of Mus Castorides. 
anterior part of the zygomatic arch, and in the remarkable pro- 
cess of the lower jaw. 
. For these reasons I have referred it to the genus Mus; but 
some more skilful hand may hereafter designate it with greater 
propriety. ‘Though nearly allied to both, it certainly differs 
_ generically from either the rat or beaver, and, in the hind feet, 
from, I think, all other Mammalia. - 
Such instances as this, the Felis jubata, and some recent acqui- 
sitions, show that there is much necessity for new intermediate 
generain the Linnwan system: whenever these shall be arranged, 
the situation of the present subject willof course easily be found. 
I have ventured to give the specific name “ Castorides," and 
to call this the ** Beaver Rat,” rather than the .M. Coypus, whose 
resemblance to both is not so great. 
- The following description is, to the best of my knowledge, 
tolerabl y correct. 
Mus CasTORIDEs. 
Mus, caudä mediocri terete squamatä subpilosä, plantis 
palmatis.. : 
Longitudo corporis 21 pollicum, caude 83. 
Color cinereo-fuscus, subtus flavescens ; pili breviores crassi, 
molles, cinerei, longiores fusci flavo annulati: auricule 
rotundate, nude: oculi parvi: mystaces longissimi, 
rigidi: dentes primores superiores 1 pollicem zequant, 
inferiores 11: pedes pentadactyli, planta palmata digi- 
tis externis en? separatis. 
In addition to the above characters it may be remarked, that 
the nose is surrounded with whitish hair, that there are a few stiff 
bristles at the base of each claw, that the thumb is extremely 
short and the claw thick, that the length of the middle claw of 
the fore foot is one inch, and that of the metatarsus three inches. 
| The 
