162 MURID#, MURINZ, MUS. 
and the consequent angles and loops shown, more readily indicate 
the relationship of their owner to other forms. Members of the 
Muridé have a certain family resemblance to each other, in the more 
or less lengthened tail, generally naked and scaly, bright eyes, and a 
modest coloration suitable for concealing them from their foes. 
Fam. Ill. Muridz. Rats, Mice, Voles, ete. 
Premolars none; molars with or without roots, tuberculate, or 
with enamel folds; lower incisors compressed; frontals greatly con- 
tracted anteriorly. 
Subfam. I. Murine. 
Molars rooted, tuberculate; root of under incisor creating a swell- 
ing on outer side of mandible between processes of the condyle and 
coronoid; descending process of mandible below the plane of the 
molars. Palate nearly flat. 
The genus Mus, has more members than any other of the Mammalia 
and its representatives are found throughout the world, except in 
Madagascar, and possibly other islands whose faune are unknown. 
The habits of the various species are similar, although some are 
arboreal and others even aquatic. 
40. Mus. Mice, Rats. 
So 
Mus Linn., Syst. Nat., 1, 1758, p. 59; UM, 1766, p. 79. Dypemems 
rattus Linneus. 
Ears large, prominent; tail long, scaly; nose acute; molars with 
transverse series of tubercles, three in a series, longitudinal. 
KEY TO THE SPECIES AND SUBSEECIES 
A. Size small; tail moderately long. PAGE 
a. Pelage above grayish brown and black, 
beneath ashy. plumibeousi ocr saree M.musculus 162 
b. Pelage above black, beneath buffy gray..... M. m. jalape 163 
B. Size large, tail very long, naked, scaly. 
a. Pelage black on ‘upperparts. - 1 ..6o-= see M. rattus 163 
b. Pelage brownish on upper parts. 
a.’ Under parts ashy white................JM. norvegicus 164 
b:’ Under partspyellowish white... so. VW. alexandrinus 164 
119. musculus (Mus), Linn., Syst. Nat., 1, 1758, p: G2; ateegeee 
p. 83. Elliot, Syn. N. Am. Mamm., rgor, p. 118. 
