AXIAL SKELETON OF THE PELECANIDA. 357 
bounded above by an antero-posterior ridge. This lateral groove ends preaxially in a 
small, but deep, fossa enclosed externally by the external root of the styloid process. 
The NINTH VERTEBRA (Plate LVIII. figs. 23-27) is very much shorter than the eighth, 
being scarcely, if at all, longer than the axis. It agrees with the ninth vertebra of Pha- 
lacrocorax in being the one to present the marked contrast, to be the first pressed back 
postaxiad at its preaxial part, and to be articulated with its two adjacent vertebree at angles 
both open dorsad. It thus agrees with the eighth vertebra of Pelecanus and of Sula. 
Here in Plotus is a hemal arch for the first time developed, and developed suddenly, 
and at once in its completeness. It extends much preaxiad of the centrum, while 
neither pair of zygapophyses may extend quite as far, pre- and postaxially respectively, 
as does the centrum; the prezygapophyses never do so. 
The neural arch is much cut away preaxially ; and the preaxial articular surface of 
the centrum looks mainly dorsad. The przezygapophysial surfaces look mediad and 
very slightly postaxiad. These processes are produced dorsad and postaxiad like those 
of the tenth vertebra of Phalacrocorax and the ninth of Pelecanus. 
The neural spine is very small, and close to the concave postaxial margin of the 
neural arch. Hyperapophyses are more developed, and have retreated preaxiad from 
the ends of the postzygapophyses. In Plotus anhinga, immediately in front of each 
hyperapophysis is another small process (fig. 24, hp’), of smaller size; to this one end 
of a strong tendinous arch is attached, the other end of which is implanted in the dorso- 
postaxial angle of the preezygapophysis of the same side. In P. nove-hollandie this tendon 
is ossified, forming a bony arch. ‘These bony arches arise from a point on the dorsum 
of the neural arch which seems to represent spine and hyperapophysis; and no neural 
spine is developed. Preaxially each arch goes to the metapophysial prominence outside 
the prezygapophysis. We here find, for the first time in the series, a conspicuous 
lateral canal, which is short, and opens preaxially dorsally to the centrum. Oblique 
metapophysial ridges project from the outer surface of the prazygapophyses. The 
hemal arch is notched medianly preaxially, with a small, ventrad, median prominence 
behind it. The styloid processes reach almost to the postaxial end of the centrum. It 
is hard to say whether they are catapophysial or parapophysial in nature; but marked 
catapophysial ridges bound on each side the median, subcentral canal. 
The TENTH VERTEBRA (Plate LVIII. figs. 28-30) is slightly longer than the ninth, and 
is like it except that the postaxial margin of the neural arch is a little more concave, 
that there is no neural spine, that the hyperapophyses are larger, the styloid processes 
are shorter, the outside of the preezygapophysis is more rugged, and the postzygapophyses 
begin always to project again a little postaxiad of the postaxial end of the centrum. 
The hemal arch has a strong median ridge running antero-posteriorly on its ventral 
surface ; and the catapophysial ridges (bounding laterally the median, subcentral groove) 
are, as usual in Plotus, strongly marked. 
The ELEVENTH veRTEBRA (Plate LVIII. figs. 31 & 32) is of about the same length as 
3c 2 
