562 U. Ss. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
are six horizontal rows of whiskers, the central with the most bristles. There is a short series, 
also, over the eye and under the chin. 
The thumb of the fore foot is quite rudimentary, with a distinct claw as broad at the base, 
but little more than half as long as the second claw. The third claw extends considerably the 
furthest ; the fourth is a little shorter; the second and fourth claws reaching to the end of the 
bulb of their adjacent fingers. There are two very large tubercles at the base of the hand, 
nearly of equal size, separated by a deep groove ; anterior to these on the palm are three others, 
the exterior at the bases of the second and fifth fingers ; the central one between the bases of the 
third and fourth. The hind feet appear as if twisted slightly, the inner edge being consider- 
ably posterior to the outer, although the anterior edge of the foot is really formed by the fourth 
metacarpal. This arrangement enables the animal to “‘ feather the oar,”’ technically speaking, 
or bring the foot forward in swimming. The fourth claw extends rather the furthest; the third 
is but little shorter ; the second a little shorter still; the tip of the first and fifth claws do not 
reach the bases of those adjacent to them. The hind claws are all short, compressed and deep, 
not much curved and rather blunt: the fore claws are similar but not so deep. There is one 
very large elongated tubercular -callosity on the inner edge of the base of the metatarsals. 
Anterior to these, there are three quite small depressed tubercles, situated respectively at the 
base of the first toe, the base of the second toe, and between the bases of the fourth and fifth ; 
none to the third toe. The under surface of all the feet is entirely naked, the skin of the 
hinder black and finely wrinkled, as if possessed of much tactile sensibility. All the feet have 
a distinct web between the basal half of the digits; their upper surface is covered with very 
short lustrous hairs, and the edges of the feet and digits generally, especially behind, are cili- 
ated with close laid stiff bristly fringes. 
The tail is cylindrical at the base, but almost immediately becomes greatly compressed, 
especially on the middle half, where it is from two to three times broader than high, the dispro- 
portion increasing posteriorly. When the tail is stretched out, the upper and lower edges are 
gently convex, the tip somewhat pointed; in its natural position, however, the tail is sickle- 
shaped, the lower edge concave. The tail can be bent into a complete circle in a vertical plane 
towards the belly, but is capable of but little flexion upwards and backwards. The skin of the 
tail is entirely black and covered with small isolated but contiguous hexagonal scales, arranged 
in quincunx, without any traces of annulations or whorls; at first sight it appears naked, but 
sparse hairs may be detected, most abundant along the upper and lower edges and the tip. 
The uncovered portion of the tail is nearly as long as the body without the head. 
The hair is of two distinct sorts; the basal, long, silky, fine, and slightly wrinkled; this is 
very close and compact, especially on the belly ; it is light bluish gray, except at the tips, which 
are light rusty brown. Interspersed among this and concealing it on the upper surface, are 
longer coarser hairs, which are of a rich chestnut brown on the belly and sides of head and 
body. The upper parts generally, from the nose to the tail, as well as the outside of the hind 
legs, are very dark brown or nearly black, with paler hairs intermixed anteriorly, and on the 
thighs ; on the lower part of the back the color is uniform. 
The preceding description was taken from a specimen (No. 951,) before being skinned, The 
following measurements were also made while the animal was fresh. 
