PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 



49 



in life it doubtless had a considerable convexity below, the front end turned upward. 

 The dilated end is concave above, convex below, and grooved on each side for 

 the attachment of the clavicle. 



Clavicles: Both clavicles are entire and firmly attached to the interclavicle, 

 but are compressed and somewhat distorted. Figures 29 b and c have been made 

 from an isolated specimen which agrees perfectly and is undistorted. As seen, the 

 mesial extremity is only a Uttle dilated in comparison with the clavicles of both 

 Varanosaurus and Dimetrodon. Of this extremity, the upper side is moderately 

 concave, the lower convex, and both sides have conspicuous radiating ridges and 

 grooves, more pronounced near the margins. The slender stem turns upward and 

 outward, in the articulated position, at an angle of about 130 degrees. As articu- 

 lated, the upper ends are about 125 mm. apart. The front border is thickened 

 throughout; the posterior border of the dilated part is thin. Beyond the dilated 



Fig. 29. — Ophiacodon mirus Marsh, X /4. A, clavicular girdle from below; B, right clavicle from in 

 front; C, right clavicle from within; D, right scapula-coracoid, outer side. 



part, on the posterior side, there is an everted, thin flange, which overlaps the lower 

 front border of the scapula. Distally the shaft for a short distance is oval in cross- 

 section, the posterior border only a little thinner and without a surface for attach- 

 ment to the scapula. Still more distally the outer anterior side is flattened and 

 grooved, and striate, as though for the articulation of a slender cleithrum, of which, 

 however, no definite evidence has been found in the specimen. 



Scapula-coracoid: The scapula-coracoid of the right side is very little dis- 

 torted (fig. 29 d). The front border of the scapula, however, was so intimately 

 united to the clavicle that it could not be recovered entire. On the left side the 

 scapiila lay over the humerus in part, and was pressed outward in its middle por- 

 tion; its outline, however, was complete, and it has been used to complete the 

 figure as shown. On both sides the scapulae lay nearly or quite in position in the 

 skeleton; that of the right side had been pushed downward and forward an inch 

 or two beyond the position occupied by the left one, whose distal margin crossed 

 the base of the spine of the eighth vertebra. 



