404 



G, R. Wieland — ArcTielon ischyros. 



Procoracoscapular. — The procoracoscapular strongly resem- 

 bles that of Protostega, the chief differences being that while 

 the scapula of ischyros is rotund on the outer side, that of 



Protostega giGtAS Tope. — 1. Right Scapuloprocoracoid, one-tenth natural size. 

 And from same individual as Plate VI. 



Archelon ischyeos. — 2-7. All from the same individual as Plate VI, and. 

 one-tenth natural size, except 6 and 7, which are one-sixth. 



2. Left Procoracoscapular, approximate outer view, 



3. Left Coracoid Procoracoscapular, approximate outer view. 



4. Left Humerus, inside view. 



5. Portion of a Marginal. 



6. Third or fourth Cervical Vertebra, front view. 



7. The same, side view. 



Protostega has a well-marked longitudinal depression near the 

 middle and a shoulder-like expansion of the outer edge of the 

 distal end. On the contrary, however, while the shaft of the 

 procoracoid of Protostega is quite regular in outline, that of 



