AXIAL SKELETON OF THE PELECANIDA. 365 
Phaéton), on the other hand, there is no such interruption, the transverse processes 
being continuously developed throughout these vertebre. 
But the most marked distinction obtains with respect to the cervical vertebre. In 
all the Pelecanide a sudden change takes place in the form of the cervical vertebre, 
no vertebra being pressed back at its preaxial end before the eighth or ninth, while the 
seventh or eighth exhibits, for the first time, serially, a postaxiad forking of its neural 
arch. In Fregata and Phaéton, on the other hand, the change in the shape of the 
vertebre is gradual, and not sudden, the fifth vertebra being already pressed back post- 
axiad at its preaxial end, while the same vertebra, or even the fourth, has already its 
neural arch forking postaxiad, and therefore with a deeply concave postaxial margin to 
its neural arch. Again, in all the Pelecanide the two ilia meet medianly in front of 
the acetabula and develop a median dorsal ridge, while in Mregata they do not nearly 
meet together medianly in that region at all. In Phaéton, though they may appear so 
to meet, yet they do not do so really, but each ilium has its mediad marginal ridge 
distant from that of its fellow of the opposite side, though the membrane intervening 
between the two may become ossified, and so produce a more or less deceptive appear- 
ance of similarity to the structure of the Pelecanide in this respect. Finally, in the 
Pelecanidz there is but a single lateral xiphoid process on each side, while in Phaéton 
there are two on each side, in addition to the median xiphoid process. 
For all these reasons [ think it better to keep the genera Fregata and Phaéton apart, 
and, confining myself here to noticing their great distinctness (with respect to the axial 
skeleton) from the Pelecanidee, to reserve any possible consideration of their positive 
affinities till I come to treat of such group as may appear to exhibit similar cha- 
racters. 
Dr. Brandt, in his paper before referred to, considers the resemblances and affinities 
of the Steganopodes amongst themselves and with other bird groups. But he bases his 
estimates upon comparisons of other parts of their anatomy, scarcely making use of 
characters drawn from the postcranial part of the axial skeleton. It seems to me 
that though the four genera described form together a very natural group, yet it is 
difficult to unite together any two of them to the exclusion of the others. Though in 
some respects Sula resembles Pelecanus more than the other genera do, yet in other 
respects Plotus and Pelecanus are most allied; and while Sula and Phalacrocorax 
might from some axial characters be associated together, yet in others (e.g. in the 
number of vertebre and in the fact that it is the ninth from which its neighbours bend 
dorsad) Phalacrocorax and Plotus may claim kinship. On the whole Plotus is the most 
exceptional and differentiated type, and should therefore, I think, form one end of the 
series, which may be begun with Pelecanus, which in some points, at least, appears the 
least differentiated and most generalized form. 
The characters of the four genera, and of the family they compose, may stand as 
follows :— 
3D 2 
