e _Delphinidae_. Flippers small, ovate, with five
digits moderately well developed. A small obtuse dorsal fin situated
considerably behind the middle of the back. Longitudinal grooves on
each side of the skin of the throat, diverging posteriorly, and nearly
meeting in front. In external characters and habits the whales of this
group closely resemble each other. They appear to be almost
exclusively feeders on cuttle-fishes, and occur either singly, in
pairs, or in small herds. By their dental and osteological characters
they are easily separated into four genera.

In the first of these, _Hyperoodon_, or bottle-nose, there is a small
conical pointed tooth at the apex of each half of the lower jaw,
concealed by the gum during life. Skull with the upper ends of the
premaxillae rising suddenly behind the nostrils to the vertex and
expanded laterally, their outer edges curving backwards and their
anterior surfaces arching forwards and overhanging the nostrils; the
right larger than the left. Nasal bones lying in the hollow between
the upper extremities of the premaxillae, strongly concave in the
middle line and in front; their outer edges, especially that of the
right, expanded over the front of the inner border of the maxilla.
Very high longitudinal crests on the maxillae at the base of the beak,
extending backwards almost to the nostrils, approaching each other in
the middle line above; sometimes compressed and sometimes so massive
that their inner edges come almost in contact. Preorbital notch
distinct, and mesethmoid cartilage slightly ossified. Vertebrae: C 7,
D 9, L 10, Ca 19; total 45. All the cervical vertebrae united. Upper
surface of the head in front of the blow-hole very prominent and
rounded, rising abruptly from above the small, distinct snout. Two
species are known. See BOTTLE-NOSE WHALE.

The typical representative of the beaked whales is _Ziphius cuvieri_,
in which there is a single conical tooth of moderate size on each side
close to the anterior extremity of the lower jaw, directed forwards
and upwards. Skull with the premaxillae immediately in front and at
the sides of the nostrils expanded, hollowed, with elevated lateral
margins, the posterior ends rising to the vertex and curving forwards,
the right being considerably more developed than the left. The
conjoint nasals form a pronounced symmetrical eminence at the top of
the skull, p