ART. 24 NEW REPTILE PROM THE OREGON CRETACEOUS — GILMORE 3 



distinct species. From an examination of 14 practically complete humeri of 

 Ptoranodon variously distorted, it appears that pressure in the vertical direction 

 (the vertebral axis of the pteryodactyl being supposed to lie in the horiaontal 

 plane, with the wings outstretched latterly) usually crushes and shortens the 

 radial crest, while pressure in the horizontal plane not only leaves the radial 

 crest extended to its full length but also alters the head of the humerus in such 

 a way that the radial crest appears to originate farther from the proximal 

 condyle. 



It is therefore quite obvious that comparisons made with this 

 material can not be relied upon. Fortunately, a few fragmentary 

 humeri from the Cretaceous deposits of England have retained their 

 natural configurations, and they offer a better basis of comparison 

 with the Oregon humerus. 



The humerus is gently sigmoid from end to end. The ends are 

 widely expanded, the distal exceeding the proximal in its transverse 

 diameter, and planes projected through the longer axes of these ends 

 would bisect one another at nearly right angles. The head is 

 elongate, roughly crescent shaped in outline, with the longer axis 

 transverse. The articular face is convex anteroposteriorly and 

 slightly concave or saddle-shaped transversely. Much of the deltoid 

 crest is missing in this specimen, but its great development is 

 clearly apparent. 



This process springs from the outer border at some distance below 

 the head, as clearly shown in Figure 1. Its broken base has a 

 greatest longitudinal diameter of 35 millimeters. The ulnar crest 

 is strongly developed, and it springs from the inner border, nearer 

 but also below the level of the proximal end. Comparison with 

 flattened Pteranodon humeri seems to indicate a more robust develop- 

 ment of this process in the Oregon specimen, and its extension down- 

 ward on the side of the shaft appears to be greater. These differ- 

 ences, however, may be more apparent than real, for there is so 

 much variation in the Niobrara humeri that little reliance can be 

 placed in observed characters. Between the deltoid and ulnar 

 crests the ventral surface of the humerus is strongly concave but 

 becomes convex immediately below the lower border of the deltoid 

 crest. The shaft decreases in size until in the middle it has a least 

 diameter of 17.5 millimeters; distally it gradually but rapidly ex- 

 pands to the distal extremity. The distal end has suffered the loss 

 of its outer articular surface, and abrasion of the inner surfaces 

 renders their exact interpretation uncertain. There is a large de- 

 pression in the center of this end, but it is not at all comparable to 

 the deep circular foramen found in the humerus of Omithodesmus, 

 as described by Hooley.^ 



8 Quart. Jour. Geol. Soc. London, vol. 69, 1913, p. 386, pi. 39, flg. 3. 



