338 PROF. ST. GEORGE MIVART ON THE 
The interzygapophysial ridge is very much more prominent; and the outline of the 
upper border of the neural arch is strongly concave. ‘The preezygapophyses look more 
dorsad. There is a prominence outside the root of the rib-like styloid process (which 
latter is much longer relatively than in Pelecanus), separated from the rudimentary 
metapophysis (m) above it by an antero-posterior groove (Plate LVI. fig. 4). 
The FOURTH VERTEBRA repeats the general characters of the third; but the rib-like 
process is longer, the metapophysis stronger, and the hypapophysis smaller (though 
still large), with only a single groove on its ventral surface. 
‘The rirru VERTEBRA is like the fourth, but that the still plainly parapophysial rib-like 
process is slightly longer, and the metapophysis larger, with no groove on its ventral 
side (Plate LVI. fig. 5). 
The hypapophysis has become replaced by a more or less narrow median subcentral 
groove, from the sides of the wide, more preaxial, part of which minute prominences 
indicate the commencement of catapophyses or lateral hypapophyses (c). 
The sIXTH VERTEBRA (Plate LVI. figs. 6-8) is rather longer, has the hyperapophyses 
much more developed, the metapophyses more marked, and the subcentral groove wider. 
The underpart of centrum is very convex antero-posteriorly, the vertebra being, as it 
were, flexed dorsad at each end towards its ventral surface. ‘The catapophyses are more 
marked than in the fifth vertebra; and the diverging rib-like styloid processes are still 
plainly parapophysial. The vacant space between these processes and the catapophysial 
ridges of the centrum corresponds with the groove between the catapophysis and the 
parapophysis on each side of the centrum of the sixth vertebra of Pelecanus. 
The SEVENTH VERTEBRA presents similar differences to its predecessor from the seventh 
of Pelecanus, except that the postzygapophyses do not project more postaxiad, nor 
is the postaxial margin of the neural arch more concave. The hyperapophyses are 
advanced as in Pelecanus, but they generally form ridges diverging postaxiad from the 
summit of the neural spine. The styloid parapophysial processes and catapophyses 
are essentially similat to those of the sixth vertebra, but they are somewhat more 
approximated (Plate LVI. figs. 9-12). 
The EIGHTH VERTEBRA in Sula (Plate LVI. figs. 18-17) contrasts with its predecessor 
even more than it does in Pelecanus, except that the neural arch is not cut away so much 
more preaxially, that there is not so much difference as to the preaxial opening of the 
lateral canal, nor in the shape and direction of the postaxial surface of centrum. ‘The 
hyperapophyses also are less marked; and the catapophyses do not form a hemal arch. 
On the other hand, the metapophyses are suddenly very much developed, presenting a 
rugged outstanding process, irregularly flattened behind, projecting dorsad and externad 
from the dorsal part of the outside of the pleurapophysial lamella, just external to the 
preezygapophysis. 
The rib-like styloid processes are more slender, and closely approximated to the 
small catapophyses; and they have become so much more ventral and median in posi. 
