136 CARNIVORES. 
THE CoMMON SEAL AND THE GREENLAND SEAL. 
Genus Phoca. 
The common seal (Phoca vitulina) and the Greenland seal (P. grenlandica) 
may be selected as well-known examples of the genus Phoca, which is the only 
genus in the family containing more than two species. All the members of this 
genus differ from the grey seal by their smaller and more pointed teeth, but more 
especially by the circumstance that each of the cheek-teeth, with the exception of 
the first in each jaw, is implanted by two distinct roots, and has its crown composed 
of three or four compressed cusps arranged ina line. In such a tooth there is one 
large main cusp in the middle, which corresponds to the single cusp of the teeth of 
the grey seal; while in front and behind this are one or two much smaller cusps. 
The common seal, which is the only species in addition to the 
grey seal ordinarily met with on the coasts of the British Islands, is 
one of three nearly-allied forms, which in the young condition cannot always be 
Common Seal. 

SKELETON OF THE COMMON SEAL. 
satisfactorily distinguished from one another by colour alone. The three species 
in question are the common seal, the ringed seal (P. hispida), and the Greenland 
seal. All these three species are much smaller than the grey seal; the ringed seal 
being the smallest of all. The latter species can always be distinguished from either 
of the others by the greater length of the first digit in the fore-foot, which exceeds 
that of the other toes. When adult, the ringed seal is blackish grey above, with 
oval whitish rings, and whitish on the under-parts; its usual length varying from 
42 to 54 feet. The common seal, on the other hand, can be easily distinguished 
from either of the others by its more massive teeth; the cheek-teeth being very 
broad and thick, and set obliquely and close together in the jaws, instead of being 
placed in the same straight line, and separated from one another by distinct 
intervals. It is, moreover, a relatively stouter-built animal, with a larger head, 
broader nose, and shorter limbs. 
The adult of the common seal is very variable in colour, but the usual tint of 
the hair on the upper-parts is some shade of yellowish grey, with irregular dark 
brown or blackish spots; the under-parts being yellowish white, generally marked 
with smaller spots of brown. The length of the male varies from 5 to 6 feet. The 
