MORPHOLOGICAL REVISION 



79 



The shoulder girdle is best known from No. 1075 University of Chicago, but 

 the imperfect girdle of No. 4684 American Museum verifies the determinations. 

 As a whole, the thorax was very narrow; the clavicles and interclavicle are tightly 

 bound together and in the University of Chicago specimen retain their position 

 undistorted, showing the space between the clavicles to have been relatively small. 

 The shortness of the neck brought the anterior end of the clavicles very close to the 

 angle of the lower jaw. 



The interclavicle (plate 5, fig. 3) is an elongate bone, rather oval in section, 

 terminating posteriorly in a slightly rugose point. The anterior end was thickened 

 and somewhat expanded; its upper sur- 

 face was smooth, but the lower face was 

 marked by a deep notch the sides ot which 

 are formed by the thickening necessary to 

 accommodate the articular surfaces for 

 the clavicles. 



The clavicles are thickened at the 

 proximal end, where they unite with the 

 interclavicle and with each other anterior 

 to the interclavicle. The union of the 

 clavicles and interclavicle is very close and 

 is accomplished by strong interlocking 

 processes. Beyond the articulation, the 

 clavicles extend out from the interclavicle 

 horizontally for a short distance and then 

 bend sharply to the rear. There are no 

 articular faces at the point of contact with 

 the scapula and cleithrum, but where the 

 blade of the clavicle turns, the upper edge 

 is bent inward and downward, overlapping 

 the edge of the scapula. The cleithrum 

 lay on the outer side of the posterior end 

 of the clavicle. 



There are specimens of clavicles and 

 interclavicles which are so different from 

 those of the more complete skeletons that 

 they might serve as the basis of new species or genera were it advisable to establish 

 new forms on such fragmentary material. One of these (No. 4390 Am. Mus. Nat. 

 Hist. Cope Coll.) shows the clavicles with about the same relative curvature and 

 included space as those described above, but there is not the deep notch on the 

 lower face of the interclavicle. 



Another specimen (No. 4771 Am. Mus. Nat. Hist. Cope Coll.) belongs to a 

 much larger animal. The clavicles are more gently curved and there is a much 

 wider space between them. There is no evidence of distortion due to pressure, but 

 it may be that this is responsible for the lesser curvature. As the clavicle of the left 

 side only is present, the matter must remain in doubt. 



The scapula (plate 5, fig. 1, and text fig. 27) is as shown in figures. The cora- 

 coid and procoracoid are not separated from the scapula by suture. The posterior 

 end terminates in a point formed by a slight excavation of the upper border. 



A separate specimen consisting of the scapula and humerus of the left side 

 only (No. 4709 Am. Mus. Nat. Hist.) and belonging to a large species of the genus 

 permits of the best description. The anterior edge is nearly straight and shows the 

 attachment of a cartilaginous epicoracoid of considerable size. On the superior 



Fie. 16. — Anterior view of the clavicles and interclavicle of 

 Diadtctes sp. X$. a, No. 4390 Am. Mus. ; b, No. 1075 

 Univ. of Chicago; c, No. 4771 Am. Mus. 



