AXIAL SKELETON OF THE PELECANIDA. 325 
vertebra. On the postero-outer ventral margin of the pleuropophysial lamella is a 
small concave fossa. This is bounded in front by a minute tubercle, which is the 
reappearance of a parapophysial process, while mediad of and behind the concave 
surface is a slight ridge, which is the serial homologue of the catapophysial ridge of 
more preaxial vertebree (Plate LV. figs. 25-29). 
From the diapophysial process a ridge runs preaxiad along the dorsum of the pleur- 
apophysial lamella, and slightly mesiad, ending preaxially in a marked antero-posterior 
metapophysial ridge, separated from the adjacent margin of the prezygapophysial 
surface by an antero-posterior shallow groove. 
The hemal arch has disappeared altogether, and in its place is a median hypapo- 
physis, which bends strongly preaxiad beneath the preaxial end of the centrum. On 
each side of this is a wide groove, bounded externally by the parapophysial tubercle, 
fossa, and ridge above noticed. 
The neural arch is not cut away obliquely; for its preaxial margin projects almost 
as much preaxiad as does the centrum. 
The neural spine is higher than in the fourteenth vertebra; and the concave surface 
postaxiad of it is much reduced in extent. 
Not only do the prezygapophyses again extend preaxiad (though only slightly so) of 
the centrum, but the postzygapophyses (for the first time since the tenth vertebra) 
extend considerably postaxiad of the postaxial end of the centrum. 
The canal for the vertebral artery is still more capacious. 
The preaxial articular surface of the centrum looks mainly ventrad (which it has not 
done since the seventh vertebra) instead of preaxiad ; and the postaxial articular surface 
looks dorsad instead of postaxiad, in this respect returning to the condition of the tenth 
vertebra. Moreover this surface is less convex transversely than in the preceding 
vertebra, and its ventral margin is less concave. 
The SIXTEENTH VERTEBRA exaggerates the characters already given of the fifteenth. 
The preaxial surface of the centrum is somewhat flattened out, less concave trans- 
versely. The ventral margin of the postaxial articular surface of the centrum is either 
very slightly concave or even slightly convex. All the zygapophysial surfaces are 
smaller. The prezygapophyses scarcely extend preaxiad of the centrum. ‘The neural 
spine is higher, and is inclined over preaxially at the summit of its preaxial end. Its 
postaxial fossa is still more reduced. ‘The dorsum of the transverse process is more 
extensive, and it extends outwards further beyond the ridge, extending preaxiad and 
mesiad from the end of the diapophysial process to the metapophysis, which latter is 
more widely separated from the prezygapophysis. 
The ventral enclosure of the lateral vertebral canal (7. ¢. the scien aptleee Jamella) 
is reduced to a delicate bridge of bone, very narrow antero-posteriorly. At the dorsal 
end of this bridge is a slightly marked and convex (articular?) surface. 
2y2 
