the Shonlder-girdh of a Plesiosaur. 339 



cliaracters of the f^onus given above, and appear to have been 

 ])ortioiis of the skeh^ton of a lar^'o (?inah^) aihilt animal. 



WhcTi the seapuhe are j)hict'(l tot^cthcr in tlieir natnral 

 position (fi^::, 2yi), a line drawn on tlieir visceral surface from 

 the tip of one dorsal ramus to the other forms an arc rather 

 greater than a semicircle. 



The left clavicle (the riijht is imi)erfect) is in tlio form of a 

 scalene triangle [r in figs. 1 and 2). Its anterior and jjosterior 

 borders are slightly concave and meet in the thickened and 

 rounded outer angle. On the ventral surface of this latter 

 are irregular rugosities, which fit into the depressions in a 

 corresponding roughened area on the uj)per surface of the 

 scapula near its outer margin, so that the two bones appear 

 to have united at this point in an imperfect loosely connected 

 suture : in some other sjjecimens I have been able to examine 

 this connexion seems to have been more perfect. This union 

 of the clavicle with the scapula is a point of considerable 

 interest, since in the Nothosauridaj and LariosauridfB the 

 outer end of the clavicle is usually suturally united with 

 the ventral plate of the scapula. The inner border of the 

 clavicle is somewhat thickened and has a bevelled edge by 

 which the bone united with its fellow of the opposite side. 

 This s^-mphysial surface presents a ridged and fibrous appear- 

 ance, quite unlike that found in the cartilage bones of these 

 animals. In all the clavicles examined this inner border, at 

 about one third of its length from the front angle, is divided 

 into two portions by an oblique notch, which runs cnitward 

 and backwaids into the bone for some distance. 



The clavicles of C. platipnerus figured by Seeley are simply 

 the parts of those bones which lie in front of this division, the 

 remainder being lost. The significance of this notch is not 

 clear ; it may either have allowed the passage of a blood-vessel 

 or may possibly mark the position of an interclavicle which has 

 either escaped notice owing to its small size or never ossified. 

 The greatest thickness of the clavicle is near the inner border, 

 where it measures 1'5 centim. through ; the whole surface is 

 marked by lines of growth which radiate from the middle 

 of the bone. Its dimensions are : — 



centim. 



Length of anterior edge 17 



„ posterior „ 14 



„ inner „ \'l 



When the clavicle is in its natural ])Ositioti on the visceral 

 surface of the scapula its hinder border rests against the 

 front of the thick posterior portion of the ventral ramus of 

 that bone, its anterior and inner portions extending rather 



