NORTH AMERICAN PLESIOSAURS 725 



acute behind. The front border of the foramen is evidently formed 

 by the clavicles, but no median suture is visible. 



Coracoids. — The right coracoid has the proximal part of the scapula 

 in position. The two coracoids formed a deep trough, with the ante- 

 rior processes directed somewhat ventrad. The intergelenoid bar is 

 very much thickened, with a deep concavity transversely above. The 

 left bone shows, on the posterior side near the thickening, the mar- 

 gin of a foramen, as has been observed in species of Polycotylus and 

 in T. oshorni. It may be the real coracoid foramen. The glenoid 

 fossa looks directly outward in the articulated position. The clavo- 

 coracoid processes are elongate and flattened, the thickened inner 

 border beveled obliquely for symphysial union. The sutural surface 

 for the interclavicle extends on the visceral surface about two-fifths of 

 the distance to the base of the process. The anterior ends are slightly 

 thickened for cartilaginous attachment. 



The united bones of the girdle are, as stated, in this specimen 

 quite normal in position and shape, and, so far as they are preserved 

 are in the relations of hfe. The under margin of the interclavicle 

 turns upward at an angle of about ten degrees from the plane of the 

 coracoids, and the girdle is very convex transversely on the under side. 

 A much wider knowledge of the structure of the pectoral girdle in the 

 older reptiles since the publication of my first paper convinces me of 

 the correctness of the determination of the elements. The clavicles 

 and interclavicle are assuredly the same elements, and not unlike 

 those of the older reptiles. The ventral process is, furthermore, I 

 am confident, not the united procoracoid, but merely a prolongation 

 of the scapula, corresponding to the 'acromion' of such reptiles 

 as Dicynodon, etc. What has become of the procoracoid we cannot 

 positively say, but I believe that, as Seeley has suggested, it is repre- 

 sented by the portion of the coracoid in front of the foramina described. 

 If this supposition be true, the immense size of the coracoid is chiefly 

 due to the development of the procoracoid. And it is not unreason- 

 able to suppose that such a development might have occurred; the 

 two bones always meet normally in the middle, and do yet in the 

 Monotremata, and the same propelhng function of the fore limbs 

 would tend to develop strongly these parts, as it has the pubes of the 

 pelvic girdle. Furthermore, in the Elasmosauridae, the posterior 



