SHUFELDT : OSTEOLOGY OF THE STEGANOPODES 147 



nally grooved nearly its entire length for a tendon going to the fingers. This is best 

 marked upon the distal moiety of the bone. The metacarpal of the middle digit is 

 also straight for the major extent of its course; its extremities becoming enlarged in 

 order to allow it to make the usual connections with the metacarpal index. It is 

 rather slender and develops no special processes, as it sometimes does in other rep- 

 resentatives of the class. 



The expanded portion of the proximal joint of the index digit is not perforated, 

 not even by the numerous pneumatic foramina which are irregularly scattered 

 over its surface. Below it is produced as a notable process, and a process that is 

 seen in some of the extinct birds, as, for instance, in Ichthyornis. The shaft of 

 this phalanx is broad and flat anteriorly, and perfectly straight from above down- 

 ward. 



Equal to half the length of the carpo-metacarpus, the distal phalanx of the index 

 digit is of a trihedral form, with an extensive excavation at the posterior aspect 

 of its proximal end, which is continued in a lesser degree the entire length of the 

 bone. It bears no claw below, but is finished off by a distinct little process. 



The pollex phalanx has very much the same form as the one just described, but 

 it lacks the longitudinal excavation down its posterior aspect. Both of the bones are 

 pneumatic. Lastly, we have the smallest phalanx of all, belonging to the middle 

 finger. This, as usual, is behind the broad proximal joint of the index, and not 

 quite equal to half its hinder border in length. 



Now the general characters of the bones of the pectoral limb are, in Sida cyanajps, 

 S. piscator, S. gossi and S. brewsteri, in the main about the same as they have just 

 briefly been given for Stila bassana. We find differences, to be sure, but they are 

 very slight. The humerus in S. cyanops closely resembles that bone in S. bassana, 

 only it is considerably smaller in the first-named species. Occasionally about the 

 proximal end of the carpo-metacarpus the position and size of the pneumatic open- 

 ings may vary, but that is often seen to be the case in all large birds with highly 

 pneumatic skeletons. 



In S. piscator the olecranon fossa of the humerus is comparatively larger and 

 with better defined borders than it has in S. bassana. This is likewise the case in 

 Sula gossi and S. brewsteri, in both of which species that fossa is especially well 

 marked. Beyond such trivial departures as these, we meet with little or nothing 

 worthy of formal record. Individual specimens of the same species, however, vary 

 a little ; take, for example, the carpo-metacarpus. It is seen to be rather smaller 

 than that of another specimen of the same species of S. bassana now at my hand for 

 comparison. 



