Yol. 56.] ARISTODESMUS EUriMEYERI. 629 



the other. They may have diverged a little posteriorly, like the 

 bones in Echidna. 



The external surface of the right precoracoid is a little longer 

 than wide. Its inner border is convex from before backward, so as 

 not to correspond with the contour of the interclavicle. The 

 external border has a lateral notch in the middle : this appears to 

 divide the thickened posterior part, which adjoined the scapula, 

 from the anterior part. A similar notch 13 seen in the precoracoid 

 of Procolophon, and apparently in Keirognalhus ; but the conditions 

 are dissimilar in Pareiasaurus, Rkopalodon, etc., in which a foramen 

 is developed at the junction of the precoracoid and coracoid, and 

 not between the precoracoid and scapula as in the other known 

 Anomodont genera. Tho external surface of the precoracoid is 

 flat, with the internal and posterior margins slightly raised. The 

 internal articular edge of the precoracoid is vertically truncated, in 

 the manner seen in the expanded coracoid bones of the shoulder- 

 girdle in Plesiosaurs and Ichthyosaurs, forming a narrow edge which 

 is rough and cartilaginous. 



The coracoid is nearly as long as the precoracoid. Its trans- 

 verse width as preserved is less. It is a somewhat lunate plate, 

 convex on its interior margin, with the posterior margins retreating 

 outward in a convex curve. The bone appears to be flattened on its 

 visceral surface. The external border is divided into two parts : 

 the anterior half forms the articulation for the humerus. But 

 behind this thickened border the bone appears to be concavely 

 notched on the side. 



It is not certain that these bones came into median contact. 

 They may have united with a cartilaginous sternum, but there is 

 no evidence of such a structure. 



(0) The Scapula. 



The right scapula extended dorsally over the ribs, above the 

 coracoid and precoracoid. The bone is moderately long, curved in 

 length, so as to be adapted to the ribs, inclined a little backward, 

 compressed from above downward. Its thickness augments from 

 the middle length to the humeral articulation. The free extremity is 

 transversely truncated, and the middle length of the blade narrower. 



At the proximal end the width is divided into two articular parts : 

 an anterior, sutural, precoracoid portion, and a posterior, glenoid, 

 humeral portion. The posterior margin is the more concave, thicker, 

 and more regularly rounded. The anterior lateral margin is nearly 

 straight, and compressed to a sharp edge. The external surface of 

 the bone is flattened, as in Pareiasaurus and Rhopalodon, and gives 

 no indication of a twist such as elevates the anterior margin of the 

 bone in African Thecodonts, and apparently in some Dicynodonts. 

 There is an imperfectly preserved anterior mesoscapular thickening 

 or slight acromion-process on the middle of the anterior border of 

 the bone. The bone is not unlike the scapula of Pareiasaurus in 

 proportion ; the acromion appears to have been similarly placed. 



