22 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



ences of importance. In Diadiaphortis the blade is high, narrow and of 

 subquadrate outline, and across it the prominent spine pursues an oblique 

 course, dividing it into two nearly equal, triangular areas. Of these, the 

 anterior, or prescapular fossa is wider distally, while the postscapular fossa is 

 wider proximally. The neck is broad, especially the portion in front of 

 the spine, and the glenoid cavity is a simply concave oval, with the antero- 

 posterior diameter somewhat exceeding the transverse. The coracoid is 

 a large and rugose, but not conspicuous, rounded tubercle. There is a 

 distinct, though shallow, coraco-scapular notch, above which the coracoid 

 border is strongly convex and curves gradually into the suprascapular 

 border. In the only available specimen of the scapula of Diadiaphorus 

 the postero-superior portion is broken away, but the strongly inclined 

 course of so much of the glenoid border as is preserved, indicates that the 

 proximal portion of the postscapular fossa was very broad. 



The spine is prominent and recurved, making the anterior surface convex 

 and the posterior concave. There is a single, well-developed metacromion, 

 which is much more distal in position than that of the Macrauchenidae ; 

 the acromion itself is broken and may not have been continued distally, 

 but, nevertheless, stands out very prominently from the neck. This is in 

 marked contrast with the Perissodactyla, in which the spine dies away 

 gradually upon the neck. 



No trace of a clavicle has been found in this or any other representative 

 of the Litopterna. 



The humerus (PI. IV, figs. 6, 6a) is short and stout, with large head 

 projecting prominently behind the plane of the shaft ; the great tuber- 

 osity is high and the deltoid ridge is very long, extending down more 

 than half the length of the shaft, upon which it dies away gradually, 

 not forming any prominence or hook. The distal trochlea is rather narrow 

 and of very simple form, without division into separate facets, and the 

 internal border has a very prominent flange for the ulna. Both the an- 

 coneal and the supratrochlear fossae are small, but deep, and are connected 

 by an irregular perforation ; the external epicondyle is distinct, while the 

 internal one is obsolete, but the postero-internal angle of the distal end 

 is a prominent rugosity, somewhat as in the horse ; the supinator ridge 

 is distinct, though not prominent. 



The fore-arm bones are quite short in relation to the humerus and are 

 in contact for most of their length, making but a short and narrow radio- 



