AXIAL SKELETON OF THE PELECANIDJ?. 357 



bounded above by an antero-postevior 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 vertebrae at angles 

 both open dorsad. It thus agrees with the eighth vertebra of Pelecanus and of Sula. 



Here in Plotus is a haemal 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 prgezygapophyses never do so. 



The neural arch is much cut away preaxially ; and the preaxial articular surface of 

 the centrum looks mainly dorsad. The praezygapophysial 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, 7j/), 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 prsezygapophysis of the same side. In P. novce-hollandice 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 prsezygapophysis. 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 praezygapophyses. The 

 haemal 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 prtezygapophysis is more rugged, and the postzygapophyses 

 begin always to project again a little postaxiad of the postaxial end of the centrum. 

 The haemal 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 



3c2 



