350 PEOr. ST. GEORGE MIVART ON THE 



vertebree — the thirty-first and the thirty-second, — although there may be as many as 

 three, or sometimes, apparently, but one. 



The Sacral Vertebrae. 



Of these there are at most but two, the thirty-third and the thirty-fourth. 



They differ from those of Sula in that, though the first has, like that of Sula, its 

 parapophysis detached from more dorsal ossification, that of the second (thirty-fourth 

 vertebra) often, if not generally, has its parapophysis continuously ossified with what is 

 dorsal to it, so as to constitute a little subvertical sheet of bone formed of parapophysis 

 and diapophysis conjoined (Plate LXI. fig. 1). 



The Sacro-caudal Vertebrje. 

 These are seven or eight in number, from the thirty-fifth to the forty-second 

 inclusive (Plate LXI. fig. 1). The condition of their parapophyses is generally inter- 

 mediate between Pelecanus and Sula, not even arising so ventrally as in the former and 

 not generally bent up dorsad so suddenly as in the latter, except in the thirty-fifth 

 vertebra, where they are quite so. Their general appearance, however, is more like 

 that presented by Sula than by Pelecanus. They are subequally developed as to the 

 transverse extent of their parapophyses ; and the last two considerably increase in antero- 

 posterior extent. 



The Caudal Vertebra. 



These vertebrae, from five to eight in number, rapidly increase in transverse diameter ; 

 and the second may have a hypapophysis, while the third has generally a distinctly 

 bifurcating hypapophysis, which becomes much larger in the succeeding two vertebrae. 

 Each vertebra has a pair of small zygapophyses (Plate LXI. fig. 5). 



The pygostyle is very diff'erent in shape from that of either Pelecanus or Sula. It 

 is much shorter and sharply bent up dorsad upon the free caudals ; its ventro-postaxial 

 margin is gently concave, and its dorso-preaxial one gently convexo-concave postaxiad — 

 both as in Sula ; but it is a very much shorter bone, and may even approximate in 

 outline to an equilateral triangle, though it may be a triangle of which the breadth is 

 but half the length. 



The Pelvis. 



This includes as many as from fifteen to seventeen vertebrae. It more nearly resembles 

 that of Sula than that of Pelecanus, but is more elongated antero-posteriorly. 



Viewed laterally it agrees with Sula, and differs from Pelecanus in the points men- 

 tioned in describing Sula, except that the sacro-iliac ankylosis is longer, and the ilio- 

 caudal spine is a very long pointed process (Plate LX. fig. 6). 



Compared with Sula, the sciatic foramen is more pointed postaxially, and, as in 



