re are from eight to ten
pairs of teeth in each jaw, occupying the anterior three-fourths of
the rostrum and corresponding portion of the lower jaw, rather small,
conical, and pointed when unworn, but usually become obliquely
truncated, separated by intervals considerably wider than the diameter
of the tooth, and implanted obliquely, the crowns inclining forwards
especially in the upper jaw. Skull rather narrow and elongated,
depressed. Premaxillae convex in front of the nostrils. Rostrum about
equal in length to the cranial portion of the skull, triangular, broad
at the base, and gradually contracting towards the apex, where it is
somewhat curved downwards. Vertebrae: C 7, D 11, L 9, Ca 23; total 50.
Cervical vertebrae free. Flippers broad, short and rounded, all the
digits being tolerably well developed, except the first. Anterior part
of head rounded; no distinct snout. No dorsal fin, but a low ridge in
its place. See BELUGA.

In all the remaining genera of _Delphinidae_ the cervical region of
the vertebral column is very short, and the first two, and usually
more, of the vertebrae are firmly united. The common porpoise
(_Phocaena communis_, or _P. phocaena_) is the typical representative
of the first genus, in which the teeth vary from 18/18 to 25/25, are
small, and occupy nearly the whole length of the rostrum, with
compressed, spade-shaped crowns, separated from the root by a
constricted neck. Rostrum rather shorter than the cranium proper,
broad at the base and tapering towards the apex. Premaxillae raised
into tuberosities in front of the nostrils. The frontal bones form a
somewhat square elevated protuberance in the middle line of the skull
behind the nostrils, rising above the flattened nasals. Symphysis of
lower jaw very short. Vertebrae: C 7, D 13, L 14, Ca 30; total 64.
First to sixth cervical vertebrae and sometimes the seventh also,
coalesced. Flippers of moderate size, oval, slightly sickle-shaped,
with the second and third digits nearly equal in length, and the
fourth and fifth well developed, but shorter. Head short, moderately
rounded in front of the blow-hole. Dorsal fin near the middle of the
back, triangular; its height considerably less than the length of the
base; its anterior edge frequently furnished with one or more rows of
conical horny tubercles.

The porpoise, which is so common in British waters and the Atlantic,
s