AXIAL SKELETON OF THE PELECANID2. 319 
No process extends postaxially from the postaxial margin of the pleurapophysial 
lamella. 
The mrTH veRTEBRA differs as much from the fourth as the corresponding one of 
Struthio differs from its serial predecessor, except that the preaxial margin of the neural 
arch is not more concaye, and that there is no noteworthy difference as to the develop- 
ment of the metapophyses. 
In addition to these points, in which it differs like the fifth of Struthio from its pre- 
decessor, it also differs from the fourth vertebra in that the whole ventral surface of 
the centrum is deeply channelled medianly and antero-posteriorly, two parallel ridges 
running postaxially from the two catapophyses (Plate LV. fig. 5). 
The lateral vertebral canal is of about the same length as in the ‘fourth vertebra ; and 
therefore the part of the vertebra postaxial to it is slightly longer. The hyperapophyses 
are developed to about the same degree as in the fourth vertebra; and the styliform 
rib is not longer. Both this vertebra and the first differ from the corresponding 
vertebre of Struthio and Dromeus in that the postaxial margin of the neural arch is 
not nearly so concave, and that the neural spine is not excavated either pre- or post- 
axially. The increase in length of this vertebra over the fourth is less than in Struthio; 
it unites with its serial predecessor at a very obtuse angle. 
A conspicuous foramen opens on each side of the ventral surface of the centrum, just 
behind the catapophysis; it leads into the lateral vertebral canal. 
When the vertebra is viewed ventrally a wide shallow median groove is seen, bordered 
on each side by a continuous catapophysial ridge. Outside the anterior third of each 
catapophysial ridge is an antero-posterior (fig. 5, y) groove separating this ridge from 
the postaxially extending parapophysial rib-like process. 
The sIxTH VERTEBRA (Plate LV. figs. 6, 7, 8) closely resembles the fifth, and is of 
nearly the same size. It differs from the fifth as does that of Struthio from its pre- 
decessor, except that, when viewed dorsally, the neural surface of the centrum is not 
more exposed at the preaxial end of the vertebra, and that catapophyses do not here 
begin, but only increase a little insize. The subcentral antero-posterior groove is deeper 
and more strongly bordered. At its preaxial end the catapophysial antero-posterior ridges 
project mesiad (fig. 8, ¢), and draw inward (as it were) somewhat the parapophysial styloid 
processes, which are here less developed than in the fifth vertebra, and are separated 
from the catapophyses by a shorter, though still very conspicuous, antero-posterior 
groove (fig. 8, g). The hyperapophyses are hardly smaller. 
The prezygapophyses project preaxiad of the centrum to a greater rather than a less 
degree than in the fifth vertebra; and the pre- and postaxial margins of the neural arch 
are not more concave, 
This vertebra differs from the fifth in the still greater production ventrad of the 
lateral margins of the subcentral antero-posterior groove, and in the somewhat more 
