144 MAMMALIA. 
Fewer species have been observed of the size of the Mouse. 
M. cahirinus, Geoff., Descr. de VEg. Mammif. (The Cairo 
Mouse.) Spines on the back in place of hairs—noticed by 
Aristotle. 
One species only is known in France that does not reside in 
houses, the MM. sylvaticus. (Field Mouse.) Buff. VII, xli, 
which is hardly larger than the Mouse, and is distinguished 
from it by its red fur. It does much injury to trees, and some- 
times penetrates into gardens. 
It seems, however, that in some of the provinces there is a 
smaller and grey species, which has also been observed in Eng- 
land, (WZ. messorius, Shaw, Vol. II, Part 1, Frontisp.) and a 
third still more diminutive (JZ. pumilus, Fr. Cuv. Mammif.).(1) 
Warm climates produce Rats, similar in every particular to those 
of which we have just spoken, except that their tails are more 
hairy.(2) 
Gereittus, Desm.—MeEnriongs, Illig. 
The Gerbils have molars that differ very little from those of Rats, 
merely becoming sooner worn, so as to form transverse elevations. 
Their superior incisors are furrowed with a groove ; their hind feet 
(1) To this division, most probably, belong the M. agrarius, M. minutus, M. so- 
ricinus, M. vagus, M. betulinus, M. striatus, M. barbarus, Schreb. 
- Here also should come the enormous Mus giganteus, Hardw. Linn. Trans. VII, 
XXViil. 
There should be likewise added the M. pumilio, Sparm. the M. cyanus, Molina, 
and several other species, some of which are not even mentioned by authors, and 
others which are described with too little comparison. This is the reason why most 
of the Rats of Azzara cannot be properly classed until they are re-examined. The 
same observation applies to a great many of the Rodentia of M. Rafinesque. Their 
descriptions are too short to be of any use. r 
(2) Hypudzus variegatus, Lichtenst. var. flava—Meriones syenensis, Id. to which 
must be added the .@rvicolu messor, Le Conte, Arv. hortensis, Harl. or Sygmodon, 
Say, distinguished however by hairy ears, like the Otomys. 
Another group, with hairy tails also, but whose teeth wear away faster, will in- 
clude the Hypudzus obesus, Lichtenst. the Mus ruficaudatus, Id. His Meriones se- 
' riceus should form a third, characterized by the projecting ridges of the molars, 
which alternately catch in each other. 
We then have to group the Weotoma floridanum of Say, or the Arvicola florida- 
nus of Harlan, and the Arvicola gossypina, Le Conte, two Rats which, size excepted, 
are very similar even in their colours, whose teeth, provided with roots, if worn a 
little, have crowns formed like those of the Aryicola. 
These animals, however, previous to a definite classification, require to be com- 
pletely examined and compared, internally as well as without. [See Append. IX 
of Am. Ed.) 
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