THE SEA-OTTER AND ITS EXTERMINATION 219 
of an ordinary otter. The skin invests the body as loosely 
as a pillow-case covers a pillow; and the dark brown fur 
is unrivalled for its softness, depth, and density. But 
even more remarkable is the difference between the cheek- 
teeth of the two animals. In place of the sharply cusped 
grinders of the common otter, the marine species has the 
crowns of these teeth surmounted by smooth ill-defined 
bosses, separated by narrow crack-like lines ; the one type 
having been aptly compared to freshly chipped flints, and 
the other to water-worn pebbles, Clearly such structural 
differences must be correlated with a totally different 
description of diet, and, in place of being a fish-eater, 
the sea-otter subsists by grinding up sea-urchins, clams, 
mussels, and such-like, shells and all. 
Had we living animals alone to guide us, there might 
be some hesitation in saying that the sea-otter is a highly 
modified offshoot from the stock of the ordinary otter, but 
the evidence of extinct forms indicates the probability of 
this being the case. Fossil remains of true otters occur 
comparatively low down in the series of rocks belonging 
to the Tertiary period; and somewhat higher in the scale 
are found, both in Europe and India, those of an extinct 
genus (Enhydriodon), in which the cheek-teeth are to a 
certain extent intermediate between the types respectively 
characteristic of the ordinary and the sea-otters, These 
intermediate extinct otters appear, however, to have been 
fresh-water animals, so that purely marine habits would 
seem to have been acquired only with the advent of the 
modern sea-otter. 
The geographical range of the latter on the American 
side formerly included Alaska, the Aleutian and Pribiloff 
Islands, Sitka, and Vancouver Island, and thus down 
the coast to California; while on the opposite shore it 
