186 U. Ss. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
east of the Rocky Mountains I am unprepared to say, the only specimens I have had an oppor- 
tunity of examining are all referrible to the Lutra canadensis of authors ; what is the precise 
value of the L. lataxina of F. Cuvier, from Carolina, or of the ZL. mollis of Gray, from Hudson’s 
Bay, I cannot now decide. 
The character of Lutra lataxina rests mainly, according to Cuvier, upon the straightness or 
even concavity of the superior outline of the skull, from occiput to the end of the nasal bones. 
Ihave noticed this character in a very old skull from Carlisle ; younger specimens have this 
profile rather more convex. 
The correctness of the reference by some authors of a North American otter to the Lutra 
brasiliensis is readily disproved by a comparison of specimens. The most striking difference is 
seen in the muzzle, which in the latter species is entirely hairy, except around the nostrils, 
instead of being naked, as in L. canadensis. 
The differences between the American and European otters are very appreciable, both in 
the external form and the skull. 
In Lutra vulgaris the skull is less massive, more elongated, and narrower. The muzzle and 
interorbital spaces are much narrower. The width of the muzzle behind the incisors is about 
equal to its length, measured from the anterior edge of the orbit to the anterior end of the 
intermaxillaries, while in Z. canadensis the width of the muzzle is considerably greater than its 
length. 
The most striking peculiarity of external form in the European species is the small size of the 
naked muffle compared with the American. This, in a nearly grown skin, is only about four- 
tenths of an inch wide, and about as long, instead of the eight-tenths of the other. The under 
surfaces of the feet are entirely naked, instead of having the pads separated from the toes by 
hair. The hair is composed almost entirely of under fur, the long hairs much more scattered 
than in the other. The color has in it much more of chestnut brown, like the southern mink or 
muskrat, and is not appreciably lighter beneath. This may, however, be a condition of age or 
season. 
The otter of the Pacific slope of North America differs in some tangible points from that of 
the east, and has been described as Lutra californicus by Dr. J. EH. Gray. 
List of specimens. 
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