The type-specimen of _Ziphius semijunctus_ (Cope), as already mentioned,
is a young female.[38] The most noticeable characters which it presents
are that the premaxillæ are flat proximally, and that the teeth are
small, sharp-pointed and open at the roots. The form of the teeth is
undoubtedly due to immaturity, but as the shape of the premaxillæ is
similar to that found in the nominal species _gervaisii_, it might be
thought necessary to refer _semijunctus_ to the latter species. As will
be shown later, however, this form of the premaxillæ appears to be
characteristic of the adult female of _cavirostris_, and of immature
individuals of either sex, the young, as in many kinds of animals,
resembling the adult female rather than the male.
I have been able to find but one character in the skull of _semijunctus_
which might be regarded as specific. This is that the lachrymal bone is
thick distally, and cut off square at the end. In other specimens of
_Ziphius_ examined it is thin and flat, and rounded or pointed at the
end. As there is much individual variation in the form of the lachrymal,
this peculiarity alone is, in my opinion, an insufficient indication of
the validity of the species.