rn whales), and long
nasal bones covering over the nasal chamber, so that the nostrils
opened about half-way down the beak. All the cervical vertebrae were
free. Normally the dentition in the typical genus _Zeuglodon_ (which
is common to the Eocene of North America and Egypt) is i. 3/3, c. 1/1,
p. 4/4, m. 3/3; the cheek-teeth being two-rooted, with compressed
pointed crowns, of which the fore-and-aft edges are coarsely serrated.
In the Egyptian _Zeuglodon osiris_ the number of the molars is,
however, reduced to 2/3, while some of the earlier cheek-teeth have
become single-rooted, as in the squalodonts. The probable transitional
form between the latter and the zeuglodonts is the small
_Microzeuglodon caucasicus_ described by the present writer, from the
Caucasus. As regards the origin of the zeuglodonts themselves, remains
discovered in the Eocene formations of Egypt indicate a practically
complete transition, so far at least as dental characters are
concerned, from these whale-like creatures to the creodont Carnivora.
In the earliest type, _Protocetus_, the skull is practically that of a
zeuglodont, the snout being in fact more elongated than in some of the
earliest representatives of the latter, although the nostrils are
placed nearer the tip. The incisors are unknown, but the cheek-teeth
are essentially those of a creodont, none of them having acquired the
serrated edges distinctive of the typical zeuglodonts; and the hinder
premolars and molars retaining the three roots of the creodonts. In
the somewhat later _Prozeuglodon_ the skull is likewise essentially of
the zeuglodont type, although the nostrils have shifted a little more
backwards; as regards the cheek-teeth, which have acquired serrated
crowns, the premolars at any rate retain the inner buttress supported
by a distinct third root, so that they are precisely intermediate
between _Protocetus_ and _Zeuglodon_. Yet another connecting form is
_Eocetus_, a very large animal from nearly the same horizon as
_Prozeuglodon_; its skull approaching that of _Zeuglodon_ as regards
the backward position of the nostrils, although the cheek-teeth are of
the creodont type, having inner, or third, roots. It is noteworthy
that _Zeuglodon_ apparently occurs in the same beds as these
intermediate types.

It follows from the foregoing that if zeuglodonts are the ancestors of
the true Cetacea--and the probabili