the antenasal fatty
elevation by a V-shaped groove. Dorsal fin rather large, triangular or
sickle-shaped, rarely wanting. A curiously marked brown and white
species, perhaps referable to _Lagenorhynchus_ is found on the fringe
of the Antarctic ice (see report on the zoology of the "Discovery,"
published in 1907 by the British Museum). See DOLPHIN.

_Extinct Cetacea._

At present we are totally in the dark as to the origin of the
whalebone-whales, not being even assured that they are derived from
the same stock as the toothed whales. It is noteworthy, however, that
some of the fossil representatives of the latter have nasal bones of a
type recalling those of the former. Such fossil whalebone-whales as
are known occur in Pliocene, and Miocene formations are either
referable to existing genera, or to more or less nearly related
extinct ones, such as _Plesiocetus_, _Herpetocetus_ and _Cetotherium_.

The toothed whales, on the other hand, are very largely represented in
a fossil state, reaching as low in the geological series as the upper
Cretaceous. Many of these present much more generalized characters
than their modern representatives, while others indicate apparently a
transition towards the still more primitive zeuglodonts, which, as
will be shown later, are themselves derived from the creodont
Carnivora. In the Pliocene deposits of Belgium and England are
preserved the teeth and other remains of a number of cetaceans, such
as _Physodon_, _Encetus_, _Dinoziphius_, _Hoplocetus_, _Balaenodon_
and _Scaldicetus_, more or less nearly related to the sperm-whale, but
presenting several primitive characters. A complete skull of a member
of this group from the Tertiary deposits of Patagonia, at first
referred to _Physodon_, but subsequently to _Scaldicetus_, has a full
series of enamelled teeth in the upper jaw; and it is probable that
the same was the case in other forms. This entails either a
modification of the definition of the _Physeteridae_ as given above,
or the creation of a separate family for these primitive sperm-whales.
In other cases, however, as in the Miocene _Prophyseter_ and
_Placoziphius_, the anterior portion or the whole of the upper jaw had
already become toothless; and these forms are regarded as indicating
the descent of the sperm-whales from the under-mentioned _Squalodon_.
The beaked whales, again, are believed to be independentl