so 



PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 



Fig. 30. — Ophiacodon mirus 

 Marsh. Right front leg, 

 dorsal side, X yi- 



The scapula is broad, resembling that of Dimetrodon more than that of Vara- 

 nosaurus. The posterior border is thickened and rounded, and curves upward 

 and backward. The supraglenoid fossa is broad and shallow ; it is pierced by the 

 usual supraglenoid canal. The front border is thinned throughout; it is straight 

 near the middle for about an inch, where the distal end of the clavicle is apposed. 

 Both above and below this straight border there is a shallow emargination of the 

 very thin bone. That a small cleithrum was present is possible, but not certain. 

 Lying just above the end of the left scapula is a small, thin bone, so closely applied 

 to the vertebrae that it could not be detached ; it may be a vestigial cleithrum. The 

 upper or distal border of the scapula, as usual, is truncated and convex in outline, 

 for the attachment of a suprascapular cartilage. The coracoid of Williston, the 

 procoracoid of authors, is narrow and, in its somewhat flattened condition as 



preserved on both sides of this 

 specimen, is not directed in- 

 wardly as much as in other 

 forms. The broad stem of the 

 interclavicle filled a part of 

 the interval between the two 

 bones, but it seems probable 

 that in life there was a consid- 

 erable cartilaginous continua- 

 tion of the truncate margin of 

 each coracoid. The posterior 

 coracoid, or metacoracoid of 

 Lydekker and Williston, the 

 coracoid of authors,* is of 

 considerable size, its separating suture showing con- 

 spicuously on both sides ; the suture between the ante- 

 rior coracoid and the scapula is not distinguishable. 

 It is an interesting fact that, wherever this bone 

 is ossified, the suture uniting it with the scapula and 

 anterior coracoid remains distinct much longer than 

 that between the anterior coracoid bone and the 

 scapula ; it is nearly always visible in Dimetrodon, and 

 the posterior coracoid is often found isolated. Will- 

 iston believes that this is further evidence of its dis- 

 appearance in modem reptiles, as in Varanosaurus 

 and Seymouria among the ancient ones. The bone, 

 whatever it may be, coracoid or metacoracoid, agrees closely with that of Dimetro- 

 don. Its suture passes through the postglenoid facet a little in front of its middle, 

 and not far back of the preglenoid facet, and about half an inch posterior to the 

 supracoracoid foramen. Its posterior border is thickened, concave in outline, and 

 somewhat everted. At the upper part of this border and somewhat inward from 

 the posterior end of the glenoid facet, there is a prominent process, like that of 

 Dimetrodon, Casea, Champsosaurus, etc. On the inner side of the scapula is the 

 usual subscapular fossa, with the opening of the supraglenoid foramen at its upper, 

 that of the supracoracoid at its lower end. 



Humerus: The humerus is an unusually short and stout bone for a zygocro- 

 taphic reptile, resembling somewhat in its general characters those of Diadectes and 

 Limnoscelis. It has a very broad entocondyle, a very large, hemispherical capitel- 



*Poradiscussionof the homologies of coracoids, see Broom, Anatom. Anzeiger, Band 41, p. 625, 1912. 



