WINGS OF ICHTHYORNIS AND APATORNIS. 157 



obliquely across the expansion, to end in a thickening, near the middle of 

 its margin. 



On each side of this ridge the bone becomes so thin as to be translu- 

 cent, and in specimen number 1759, the ossification appears to have been 

 incomplete, so that a minute foramen is left in the proximal thin portion, 

 and a larger foramen in the distal part of the expansion. In number 1755; 

 a small foramen exists in the distal part of the expansion only, and even 

 this may possibly have been the result of partial crushing. The distal part 

 of the expanded portion is thickened, and produced into a flattened hook- 

 like process, beyond the end of the bone, but this is broken off from most 

 of the specimens preserved. 



The proximal articular surface consists of a sub-circular shallow con- 

 cavity on the ulnar and palmar side, and a somewhat crescent-shaped 

 siuface. This crescent is blunt at the ends, and extends through a little 

 more than a quarter of a circle around the sub-circular face, so as to 

 admit only of a slight rotary motion, the joint being- somewhat like the 

 peg-and-socket articulation seen in the toes of Hesperomis. The shaft 

 of the bone is flattened on the radial side, and, on the anconal surface, 

 just beyond the middle, is a distinct scar, extending obliquely across 

 the shaft. A similar elongated scar is seen on the palmar surface of 

 the bone, near the distal end of the ulnar expansion. 



The distal articiilar face is subquadrate in outline, broadest on the 

 radial side, where it is flattened, while the ulnar portion of the face is 

 smaller and convex, and is separated by a groove from the radial part. 

 The palmar surface of the ulnar expansion of the bone is excavated proxi- 

 mally, while distally the excavation is more pronounced on the anconal 

 surface. 



The proximal phalanx of the median digit of the wing of Apatornis 

 (number 1734) is comparatively much smaller than in Iclitliyornis, and, as 

 in that genus, the shaft tapers rapidly toward the distal end. The 

 expanded portion on the ulnar side is about in the same proportion as in 

 that genus, but it is less evidently strengthened by oblique ridges. It is 

 also more nearly of uniform thickness, being barely translucent at any 



