basal tubercles, more or less developed; in a few of the largest species,
they are simple and obtuse, and particularly so in the Walrus,
in which the molar teeth are reduced to a smaller number than in the
true Seals(l). In these the line of demarcation between the true and
false molars is very indefinitely indicated by characters of form or
position; hut, according to the instances in which a deciduous dentition
has been observed, the first three permanent molars in both
jaws succeed and displace the same number of milk molars, and are
consequently premolars; occasionally, in the Seals with two-rooted
molars, the more simple character of the premolar teeth is manifested
by their fangs being connate, and in the Stenorhynchus serridens the
more complex character of the true molars is manifested in the crown.
There is no special modification of the crown of any tooth by which it
can merit the name of a ‘ sectorialbut we may point with certainty
to the third molar above, and the fourth below, as answering to those
teeth which manifest the sectorial character in the terrestrial Carnivora.
The coadaptation of the crowns of the upper and lower teeth is
more completely alternate than in any of the terrestrial Carnivora,
the lower tooth always passing into the interspace anterior to its
fellow in the upper jaw. In the genus Phoca proper (Calocephalus,
Cuv.) typified by the common Seal (Ph. vitulina), the dental formula
is :
Incisors — ; canines j ; premolars ; molars |jp : — 34.
The forms and proportions of these teeth are shown in PI. 132, fig. 1.
The first tooth above and below presents a complete confluence
of the fangs ; they are separated in the rest above ; but below they
sometimes do not become free before the fourth, and sometimes
the two roots are distinct in the third and second molars. In the
Phoca anellata, Nills : the principal cusp of the molar teeth is complicated
with anterior and posterior smaller cusps, sometimes one
in number in the upper molars; the anterior accessory cusp is sometimes
wanting in the first, and is rudimentary in the rest; but usually
(1) The relation of Trichechus to the Phocidce is analogous to that of Machairodus to the
Felida, and also, in the simplification of the molars, to the relation of Proteles to the Canidce.
there are two small cusps behind the principal one, and in the three
or four posterior molars in the lower jaw there are sometimes two
small cusps before and two behind the principal one.(l)
In the Phoca caspica the upper molars have commonly one accessory
cusp before and one behind the principal lobe, the lower
molars have one accessory cusp before and two behind the lower
molars.
In the Phoca grmnlandica the upper molars have no anterior basal
cusp and only one behind; the lower molars have two cusps behind
and one in front, except the first which resembles that above and,
like it, has connate fangs.
The condition of the molar teeth is nearly the same in the
Phoca barbata (PI. 132, fig. 2); but the crowns are rather thicker and
stronger, a.nd the three middle ones above have two posterior basal
cusps feebly indicated, the same being more strongly marked in the
four last molars below.
The following genera of Seals with double-rooted molars, (Pela-
gius & Stenorhynchus), have four incisors above as well as below,
i. e. t |. An upper view of the molar teeth in the Hooded Seal of the
Mediterranean, Pelagius monachus, is given in PI. 132, fig. 3, as when
they are worn down in an old specimen; the crowns are thick, obtuse,
subcompressed, with a well developed cingulum, a principal lobe and
an anterior and posterior accessory basal lobule; the fangs are connate
in the first tooth both above and below.
The allied sub-genus (Ommatophoca) of Seals of the southern
Hemisphere has six molar teeth on each side of the upper, and five
on each side of the lower jaw, with the principal lobe of the crown
more incurved. The two first molars above are closely approximated
| but this may prove to be a variety.
In the Stenorhynchus the jaws are more slender and produced,
and the molar teeth are remarkable for the long and slender shape of
the principal lobe and of the accessory basal cusps. The incisors
have sharp conical recurved crowns, like the canines, and the exter-
(1) Nillson, in Wiegmann’s Archiv. 1841, p. 313. I notice these varieties of the crown, in
connection with analogous ones in the fangs of the teeth of the same species, to show the inadequacy
of such characters as marks of subgeneric distinction