144 MEMOIRS OF THE CARNEGIE MUSEUM 



The extremities of their diapophyses anchylose in a very thorough manner with 

 the inner ihac margins, and a lateral view shows their sides to be riddled with pneu- 

 matic foramina between these processes. 



Viewing this pelvis from above, we notice that the entire inner margins of the - 

 iliac bones have merged into and completely anchylosed with the sacrum. This 

 converts the ilio-neural grooves into ilio-neural canals and gives the bone a very 

 compact appearance. The anterior margins of the ilia are; rounded, and are set off 

 with rather a deep and raised emargination in S. bassana, which is feebly marked in 

 S. ])iscator and other species. 



The post- and pre-acetabular surfaces are about equal in the extent of their su- 

 perficial areas, except in Sula cyanops, where the postacetabular area is the more 

 extensive. 



The anterior iliac surfaces are concave on either side, and each faces upward 

 and outward to about an equal degree. Sula piscator here offers another exception, 

 and in this species the pelvis is comparatively shorter, as well as broader and flatter 

 than it is in other species of Gannets. 



Elevated above these anterior iliac concavities we find the postacetabular area to 

 be nearly horizontal. Large elliptical foramina are found between the apophyses 

 of the last three or four uro-sacrals, and these latter, likewise, develop quite a 

 prominent neural crest. 



Upon the lateral aspect of this pelvis we find a very large cotyloid ring, the 

 inner margin of which is fully equal in size to the outer. A moderately sized anti- 

 trochanter occupies its usual site, with its articular surface directed downward, 

 forward and outward. 



Behind this occurs an enormous elliptical ischiadic foramen, that occupies nearly 

 all of this post-acetabular lateral aspect. Through the fenestra thus formed we are 

 enabled to get a good lateral view of the uro-sacral vertebrae and the extensive 

 pneumatic condition they enjoy. 



The lower margin of the ilium is sharp and convex ; it forms the superior boun- 

 dary to a long, narrow, obturator space, which opens freely into the rather small 

 obturator foramen. 



A pro-pubis does not develop in the Gannets, while the post-pubis is, for the most 

 of its extent, fragile and slender-. It begins to increase in size just before arriving 

 at a point opposite the end of the ischium. At this point it offers a small facet on 

 its upper margin for the ischiadic postero-inferior angle, and the two bones are in 

 contact here during life. The post-pubis, retaining its increase in size, then curves 

 inward toward the fellow of the opposite side, to terminate in a cartilaginous tip. 



