354 PROF, ST. GEORGE MIVART ON THE 
The whole axial skeleton, when compared with those of the genera previously 
described, presents a remarkable contrast in the great prolongation of its more preaxial 
part, while its pelvic part is somewhat shortened, notably as compared with the same 
part in Phalacrocorax, with which genus, nevertheless, the axial skeleton of Plotus, on 
the whole, most agrees. Thus it agrees with Phalacrocorax in the strongly opistho- 
ccelous condition of the trunk-vertebre, and in their median, subcentral, laterally 
compressed prominences, though (as we shall see) they have not the same nature as 
the analogous parts in Phalacrocoraz. 
In the elongation of the anterior cervical vertebrae Plotus is more nearly approached 
by Pelecanus; but these bones are not nearly so long and slender relatively in the 
last-named genus, nor are they so smooth dorsally and with such rudimentary neural 
spines as in Plotus. 
Tue CrervicaL VERTEBRA. 
These vertebre, from their length and the little relative prominence of their pro- 
cesses, resemble (as has just been said) the cervical vertebre of Pelecanus; but in 
number and essential details of structure they rather resemble those of Phalacrocorax, 
presenting at the same time a number of special peculiarities. 
As has been pointed out by Professor Garrod! the vertebre are mostly long to the 
eighth, which is extraordinarily elongated (as also the third, fourth, and fifth), and 
forms an angle open ventrad with its predecessor, and an angle open dorsad with its 
successor. 
The styloid rib-like processes are little developed in the first seven vertebra, but in 
the eighth and succeeding ones much so, above all in the eighth, where their length is 
such as to extend peculiarly ventrad, aud postaxiad of the preaxial end of the hemal 
arch of the vertebra next behind, 7. e. the ninth. 
The arias is much like that of Phalacrocorax ; but there are no lateral hypapophysial 
processes, and the hyperapophyses project less postaxiad, scarcely more so than in 
Pelecanus. The odontoid foramen is smaller, relatively as well as absolutely, than 
in any of the three preceding genera (Plate LVIII. figs. 1 & 2). 
The axis differs remarkably from that of all the three preceding genera in its great 
relative antero-posterior length and little dorso-ventral extent, due principally to the 
small development of the hypapophysial element; it is also relatively less broad 
transversely (Plate LVIII. figs. 3 & 4). 
The odontoid process is very small. There is a distinct, elongated, though low, neural 
spine. The articular surfaces of the postzygapophyses project as much postaxiad as do 
the zygapophyses themselves. There is an interzygapophysial ridge. The postaxial 
articular surface of centrum looks dorsad as well as postaxiad ; and its ventral margin is 
strongly concave. ‘The ventral surface of the centrum presents three antero-posterior 
Proc. Zool. Soc, 1876, p. 336-7. 
