AXIAL SKELETON OF THE PBLECANID^. 361 



The TWENTY-FOUETH VERTEBRA (Plate LXI. figs. 6, 7, 8, xxiv) f^reatly resembles its prede- 

 cessor ; but its hypapophysial plate scarcely bifurcates at all preaxially, while its ventral 

 margin is more concave antero-posteriovly. It is extremely like the same vertebra of 

 Phalacrocorax ; and the non-identity in nature of the hypapophysial processes of the two 

 genera would never be suspected were these two vertebrse alone compared without their 

 serial predecessors. 



The TWENTY-FIFTH and twenty-sixth vertebrae are successively smaller and smaller, 

 and have the hypapophysial plate successively simpler and less developed. 



They differ from the corresponding vertebrae of Phalacrocorax in having the hypapo- 

 physial process smaller. 



The twenty-sixth vertebra may be devoid of any vertebral rib ^ ; but a sternal rib 

 always corresponds with it. 



The Lumbar Vertebra. 



These appear to be constantly four in number, with short parapophysial processes 

 ankylosing distally with the ilium, and thus intercepting between them three anterior 

 pelvic foramina on each side. These vertebrae (the twenty-seventh, twenty-eighth, 

 twenty-ninth, and thirtieth) have their centra continuously ossified together and with 

 the last two dorsal, and with the lumbo-sacral, sacral, and sacro-caudal vertebrae. The 

 centra of the lumbar vertebrae gradually broaden postaxially ; and though the first has 

 a hypapophysial prominence little less than that of the last dorsal, yet the two most 

 postaxial have a median, ventral, antero-posterior groove. The parapophyses become 

 successively shorter postaxiad. They thus present a general similarity to the lumbar 

 vertebrae of Phalacrocorax (Plate LXI. fig. 8). 



The Lumbo-sacral Vertebra. 



Of these there may be two or three ; they are the thirty-first and thirty-second 

 VERTEBRAE of my Specimen, which I have taken as my type. They are generally similar 

 to those of Phalacrocorax. 



The Sacral Vertebra. 



There seem to be constantly two of these vertebrae (the thirty-third and thirty- 

 fourth) ; but they are less differentiated from the sacro-caudals than is the case in 

 Phalacrocorax. Yet the parapophysis does descend decidedly more ventrad than does 

 the transverse process in the anterior sacro-caudal vertebrae. Moreover, as in Phala- 

 crocorax, the transverse process of at least the more posterior sacral vertebra forms 

 one continuous whole — a somewhat, though but slightly, vertically extended plate. 

 On the other hand, in the first sacral, the parapophyses may be more or less separated 

 from the diapophysis. 



' As in the specimen of Plotus anhinga in the College of Surgeons' Museum, 



