SHUFELDT: OSTEOLOGY OP THE. STEGANOPODES 141 



ribs. In a specimen of 8. bassana, however (No.!l8045 U. S. Nat. Mus.), and in one 

 of S. piscator (No. 18739, U. S. Nat. Mus.), I find but five of these facets upon either 

 costal border. There are no pneumatic foramina in the elongated and shallow 

 intervals between them. 



The principal orifices of this character consist in a diffuse group on the superior 

 aspect of the anterior projecting part, within the general concavity of the bone. 



Either costal process gracefully rises from its base as a laminated and prominent 

 horn, curving in the anterior direction. 



The posterior moieties of the lateral borders are somewhat rounded and extend 

 almost directly backward over the lateral processes behind. 



These postero-external xiphoidal processes are very long and wide, being rounded 

 off at their extremities and directed a little outward. They are narrowest in S. 

 brewsteri, more flaring in S. gossi, and very wide in S. cyanops. 



They are created by this hinder portion of the bone being so profoundly one- 

 notched that a general concave mai'gin has resulted, with simply a median papilli- 

 form process remaining. Even this latter is frequently altogether absent in S. gossi, 

 converting the posterior sternal border in this species into one long, well-marked 

 concavity. 



The carina juts out very prominently in front of the bone ; its anterior angle is 

 concave from above downward, and develops a large facet for the furcula, which in 

 life articulates with it. Above this the border is again concave and sharp, while 

 still above this there is a compressed process that represents the manubrium. This 

 is the case in S. bassana only, for in the sternum of no other Gannet before us is 

 there the slightest semblance of such a process as the manubrium. 



The lower border of the keel is straight and in the horizontal plane, being capped 

 off with a spreading rim. This border merges into the surface of the body of the 

 bone before it halfway reaches the xiphoidal notch. 



The sides of the keel are smooth, and neither it nor the under side of the sternal 

 body show in this specimen any of the muscular lines usually present in most birds. 



A broad median notch, concave from side to side, convex from before backward, 

 lies between the lofty superior portions of the coracoidal grooves. These latter meet 

 in front of it, while behind, its surface becomes directly continuous with the general 

 surface of the upper side of the body, and that where the group of pneumatic foram- 

 ina are found. 



A coracoidal groove looks forward and outward for its upper portion, directly 

 upward for its lower, and extends rather less than half way between the base of the 

 costal process and the median line. It consists of two portions which are directly 



