224 S. ir. Williston — North American Plesiosaurs. 



misinterpretation of its parts by Professor Cope, and the 

 absence of other, essential parts, it has remained until the 

 present time not well understood. Nor is it possible yet cor- 

 rectly to define it in all its details, since in no one species do 

 we know the complete skeleton ; and it is possible, even more, 

 it is probable, that there are two or more concurrent genera 

 among the following species, which may eventually have to 



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Cor 



Figure 1. — Pectoral girdle of Cryptoclidus oxoniensis Phillips. From 

 drawing of articulated specimen, American Museum of Natural History. 



be distinguished from each other. Its relationships are near- 

 est with the genus Cryptoclidus of Europe, a figure of the 

 pectoral girdle of which, copied from a drawing kindly made 

 for me from an articulated specimen in the American Museum 

 of New York City, is given herewith (text-figure 1). But the 

 two genera are very distinct. Indeed I am not at all sure but 



