1893. 



3.J Clavicular Arch in Ichthyosauria and Sauropterygia. 151 



rises in this region only two parts " one posterior, glenoid, diarthro- 

 ial segment ; the other, an anterior synchondrosial segment, which 

 articulated with the coracoid." This is a point upon which I may 

 state that in describing Ophthalmosaurus* I suggested the view which 

 Mr. Hulke has adopted. But I appeal from those disconnected bones 

 to the evidence from the specimens in museums like the national 

 collection. The Natural History Museum contains isolated scapulae, 

 but it also contains some scapulae in natural position in the 

 skeletons from the Lias, and there are other skeletons exhibiting the 

 shoulder girdle in good preservation in the Geological Museum at 

 Cambridge and elsewhere. 



z.cl 



FIG. 1. Shoulder girdle of Ophthalmosaurus. i.cl., front aspect of interclavicle ; on 

 the right is a side view of this bone, showing its ventral and visceral 

 contours. Beneath it are the posterior surfaces of the right and left 

 clavicles (CL). Below this all the bones of the shoulder girdle are put 

 together. The interclavicle is embraced by the clavicles ; and (cor.) 

 coracoid and scapula (Sc.) contribute to enclose the coracoid foramen (f). 

 On the right and lower corner is an isolated scapula, with the margin of 

 the coracoid foramen (/') completely ossified, preserving the carti- 

 laginous surface (ca.). gl., humeral articulation. 



* ' Quart. Jour. Oeol. Soc.,' 1874, vol. 30, pp. 693, 703. PI. XLV, fig. 1, is a 

 left coracoid. The surface lettered c is the humeral articulation; the surface * 

 is the intercoracoid suture. 



