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University of California Publications in Geology [Vol. 10 



ment of the caudal fin took place at a quicker pace than in the 

 mixosaurians. 



PESSOSAURUS AND SHASTASAURUS 



Of the material from the upper saurian horizon of Spitsbergen, 

 which I have tried to unite with Pessosaurus polaris Hulke, only the 

 coracoid, humerus, radius, idna and a few podial bones are found to- 



Fig. 3. — Shastasaurus osmonti Mer- Fig. 4. — Pessosaurus polaris Hulke. 



riam. Anterior limb, X % (after Anterior limb, X J /4. 



Merriam). 



C, coracoid ; H, humerus; B, radius; U, ulna; I, intermedium; T, trochanter. 



gether. As the ulna was destroyed in the preparation, I have not 

 figured it before, although a very important fragment in juxtaposition 

 to the radius is left. The bone had, however, the shape, very nearly 

 at least, that I have reproduced in the accompanying figures (figs. 3 

 and 4). This neglect on my part has doubtless contributed to the 

 peculiarities of the species, over against Shastasaurus, not having ap- 

 peared as clearly as could have been desired. A comparison between 



