180 



MARINE EEPTILES OF THE OXFOED CLAT. 



■with the scapular facet, its surface is gently concave and nearly smooth. Internal to 

 these facets the bone is greatly thickened to the median symphysis, the form of which 

 is shown on PL X. fig, 1 c. Behind this the bone thins greatly, especially towards the 

 median line, and the straight symphysis is only interrupted at about a third of its length 

 from the hinder end by a small foramen [for.) which is present in several specimens 

 examined and probably transmitted a blood-vessel. The lateral borders, which 

 are deeply concave, are somewhat thickened and terminate posteriorly in the postero- 

 lateral processes {p.e.p), which in adult individuals in this genus are strongly developed, 

 and project outwards and backwards ; they terminate in an oval concave surface, which 

 was no doubt capped with cartilage during the life of the animal, and this cartilage 



Text-fiff. 89. 



Immature shoulder-girdles of Cryptodeidits o.voniensis : A, a very young specimen with clavicles 

 restored (E. 2416) ; B, an older example. (About 4- nat. size.) 



cl., clavicle ; cor., coracoid ; gl., glenoid cavity ; sc, scapula. 



was continuous with the fringe of that substance which continued backwards the some- 

 what irregular posterior borders of the bones. The visceral surface of the united 

 coracoids is concave from side to side, and, though slightly convex from before backwards 

 in the region of the symphysial thickening, is strongly concave in that direction in its 

 posterior two-thirds. 



The above description refers to the shoulder-girdle of old individuals in which 

 ossification is in an advanced condition. Fortunately the Leeds Collection contains 

 shoulder-girdles of individuals of various ages, so that it has been possible to give an 



