80 



A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA 



edge there is a notch near the anterior end, and just posterior to this, at the point 

 where the clavicle would overlap the bone, there is a thickening of the edge. The 

 posterior portion of the upper edge is straight or slightly concave. As in all other 

 specimens no sutures can be traced between the scapula, coracoid, and procora- 

 coid. The coracoid foramen penetrates the bone just anterior to the upper end 

 of the cotylus. This latter is deep and obliquely placed, so that when it was in 

 position it held the humerus almost at right angles to the scapula and limited it to a 

 simple forward and back motion. 



The cleithrum is best described from the same specimen as the scapula. It 

 was closely applied to the posterior half of the upper edge of the scapula, the anterior 

 half being deeply grooved on the lower surface to accommodate the upper edge of 

 scapula. The posterior half is wider and thinner. 



The humerus (plate 5, fig. 2; plate 6, figs, 7, 8, 9) is remarkable for its shortness 

 and strength. The two ends are flattened and extended almost at right angles to 



Fig. it. — Diadrcres phaseolinus. X $. No. 4684 Am. Mus. 

 a, right scapula and cleithrum; b, ulna; c, radius. 



each other; there is practically no shaft, the two ends joining directly. The proxi- 

 mal articular face lies obliquely across the proximal end; its limits are well defined, 

 indicating little cartilage in the joint. The great deltoid ridge lies on the lower edge 

 of the proximal end when the bone is in position. Just distal to the deltoid ridge 

 (fig. 28) on the posterior edge of the bone, is a prominent ectepicondylar process; 

 this stands straight out from the bone and does not curve downward, as in some 

 reptiles, to form an ectepicondylar notch. The entepicondylar process is particu- 

 larly broad and strong, being equaled in this respect only by the stegocephalians 

 Eryops and Stereorhachis. At the inner distal corner of this process is a large pit for 

 the attachment of a strong ligament. The entepicondylar foramen is an elongate 

 oval. The articular surface for the head of the radius is a perfectly hemispherical 

 surface on the anterior face of the bone. The face for the ulna is iargely confined 

 to the distal end. 



Radius: The shaft is nearly straight. The upper articular face is roundly 

 triangular and the lower face is more of an elongate oval; this is partly due to crush- 

 ing (fig. 27, c). 



Ulna: The proximal end has an oblique articular face, but there is not a well- 

 formed sigmoid cavity to fit closely around the end of the humerus, as in the Pely- 

 cosaurs; it resembles much more closely the ulna of the amphibian Eryops. The 

 articular face curves over the upper end of the bone until it appears slightly on the 

 posterior surface. The shaft is a narrow oval in section. The distal articular 



