their roots only in the gum, and not in bony sockets. This, with the
frequent presence of rudimentary teeth in other species of this genus,
indicates that the beaked whales are derived from ancestral forms with
teeth of normal character in both jaws. The species are distributed in
both northern and southern hemispheres, but most frequent in the
latter. Among them are _M. bidens_, _M. europaeas_, _M. densirostris_,
_M. layardi_, _M. grayi_ and _M. hectori_; but there is still much to
be learned with regard to their characters and distribution. This
group was abundant in the Pliocene age, as attested by the frequency
with which the imperishable long, cylindrical rostrum of the skull, of
more than ivory denseness, is found among the rolled and waterworn
animal remains which compose the "bone-bed" at the base of the Red
Crag of Suffolk.

Finally, in Arnoux's beaked whale (_Berardius arnouxi_), of New
Zealand, which grows to a length of 30 ft., there are two
moderate-sized, compressed, pointed teeth, on each side of the
symphysis of the lower jaw, with their summits directed forwards, the
anterior being the larger of the two and close to the front of the
jaw. Upper ends of the premaxillae nearly symmetrical, moderately
elevated, slightly expanded, and not curved forward over the nostrils.
Nasals broad, massive and rounded, of nearly equal size, forming the
vertex of the skull, flattened in front, most prominent in the middle
line. Preorbital notch distinct. Rostrum long and narrow. Mesethmoid
partially ossified. Small rough eminences on the outer edge of the
upper surface of the maxillae at base of rostrum. Vertebrae: C 7, D
10, L 12, Ca 19; total 48. The three anterior cervicals welded, the
rest free and well developed. Apparently this whale has the power of
thrusting its teeth up and down, exposing them to view when attacked.

[Illustration: FIG. 6.--The Susu, or Ganges Dolphin (_Platanista
gangetica_).]

In a family by themselves--the _Platinistidae_--are placed three
cetaceans which differ from the members of the preceding and the
following groups in the mode of articulation of the ribs with the
vertebrae, as the tubercular and capitular articulations, distinct at
the commencement of the series, gradually blend together, as in most
mammals. The cervical vertebrae are all free. The lacrymal bone is not
distinct from the jugal. The jaws are long a