rojecting forwards over the nostrils, flat above,
prominent and rounded in the middle line in front, and separated by a
notch on each side from the premaxillae. Preorbital notch not
distinct. Rostrum (seen from above) triangular, tapering from the base
to the apex; upper and outer edges of maxillae at base of rostrum
raised into low roughened tuberosities. Mesethmoid cartilage densely
ossified in adult age, and coalescing with the surrounding bones of
the rostrum. Vertebrae: C 7, D 10, L 10, Ca 22; total 49. The three
anterior cervical vertebrae united, the rest free.

[Illustration: FIG. 4.--Sowerby's Beaked Whale (_Mesoplodon bidens_).]

In the numerous species of the allied genus _Mesoplodon_ there is a
much-compressed and pointed tooth in each half of the lower jaw,
variously situated, but generally at some distance behind the apex;
its point directed upwards, and often somewhat backwards, occasionally
developed to a great size. In the skull the region round the nostrils
is as in _Hyperoodon_, except that the nasals are narrow and more sunk
between the upper ends of the premaxillae; like those of _Hyperoodon_,
they are concave in the middle line in front and above. No maxillary
tuberosities. Preorbital notch not very distinct. Rostrum long and
narrow. Mesethmoid in the adult ossified in its entire length, and
coalescing with the surrounding bones. Vertebrae: C 7, D 10, L 10 or
11, Ca 19 or 20; total 46 to 48. Two or three anterior cervicals
united, the rest usually free.

[Illustration: FIG. 5.--Skull of a Beaked Whale (_Mesoplodon
densirostris_).]

Though varying in form, the lower teeth of the different members of
this genus agree in their essential structure, having a small and
pointed enamel-covered crown, composed of dentine, which, instead of
surmounting a root of the ordinary character, is raised upon a solid
mass of osteo-dentine, the continuous growth of which greatly alters
the form and general appearance of the tooth as age advances, as in
the case of _M. layardi_, where the long, narrow, flat, strap-like
teeth, curving inwards at their extremities, meet over the rostrum,
and interfere with the movements of the jaw. In one species (_M.
grayi_) a row of minute, conical, pointed teeth, like those of
ordinary Dolphins, 17 to 19 in number, is present even in the adults,
on each side of the middle part of the upper jaw, but embedded by