192 U. Ss. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
the lower equal, with a longitudinal groove in the posterior face. Upper molars, three on either 
side ; lower, five, the anterior sometimes deciduous. The naked muzzle depressed, produced, 
with the nostrils entirely inferior. Soles broad, naked. Tail moderate. 
Mephitis.—Upper incisors nearly equal, the outer but little the stouter. Upper molars, four 
on each side; lower, five, the anterior never deciduous. Snout srominent, not depressed ; nos- 
trils lateral. Soles rather narrow, partially or entirely hairy. 
All the North American species belong to the last division, excepting the Mephitis mesoleuca, 
which is a Thiosmus.+ 
The species of these two divisions of Mephitis are confined to America, and extend through 
both halves of the continent ; several of them are peculiar to Mexico. Of 7’hiosmus, two species 
are Mexican, one of them extending into the United States; all the rest are South American, 
where the restricted Mephitis does not occur. 
MEPHITIS (THIOSMUS) MESOLEUCA. 
White-Backed Skunk. 
Mephitis mesoleuca, LicuTENsTEIN, Darstell. neuer Saugt. 1827, 34; tab, xliv. f. 2—Is. Abh. K. Akad. Berl, for 
1836, 1838, 271; tab. i, f. 1. (Skull.) 
Waener, Suppl. Schreb. II, 1841, 192 —Is. in plates of Schreber’s Sdugt. IV, exxi, A. 
Scuinz. Syn. Mam. I, 1844, 319. 
Aun. & Bacu. N. A. Quad. II, 1851, 18; pl. liii. 
Mephitis nasuta, Benn. Pr. Zool. Soc. I, March, 1833, 39. 
Fraser, Zoologia Typica, No. 4. Plate. 
Thiosmus nasuta, Less. Nouv. Tableau R. Anim. 1842, 66. 
Sp. Cx.—A broad, uninterrupted band of white, beginning abruptly at the nape as a transverse straight line, and occupying 
the entire back to the tail, which also is entirely white. 
A single specimen of this species was collected by Captain Pope, in Western Texas. It is, 
however, in very poor condition, and does not furnish materials for an accurate description, 
owing to the loss of the hind feet, &c. 
The muzzle of this animal is elongated and much depressed ; naked for nearly an inch from 
the end above, and half as much below—the hair extending a little further than this on the 
sides. The nostrils are entirely inferior, not visible from above, or laterally. 
The upper lateral incisors are rather larger and longer than the central. The lower incisors 
with a furrow on their posterior side. According to Lichtenstein, there are but three upper 
molars ; in the skull (1886) before me, however, a fourth is visible, next to the canines, but it 
is very small and rudimeutary. 
The body of this species, as in nearly all the others, is black, with the exception of the white 
dorsal stripe. This begins op the middle of the crown, in a transverse straight line of an inch 
in width, widens rapidly, so as on the middle of the back to occupy fully half the entire circum- 
ference, contracts again to the base of the tail, where it is about two or three inches wide, and 
then passes into the tail, which is entirely white throughout. There is no black enclosed in 
the white of the back, this color being continuous throughout. 
This species is similar, in some respects, to Mephitis leuconota of Lichtenstein ; this is, how- 
' J, E. Gray, in Charlesworth’s Magazine of Natural History, I, 1837, 581, establishes two genera—Conepatus and Marputius— 
the latter of which, to some extent, covers the ground of Thiosmus, and anticipates it in point of date ; though objectionable in 
some respects, a strict regard for the law of priority may cause it to be retained. 
