Page:Popular Science Monthly Volume 53.djvu/228

 data of mosasaurs and has added four new genera. Baur gave the first complete description of the skull of a species of Platecarpus. Williston and Case first described the vertebral column and extremities and the general form of mosasaurs. The former has contributed most to our knowledge of mosasaurs in the Kansas Cretaceous, and made the first correct restoration, which is made one of the bases of this paper.

Professor S. W. Williston, University of Kansas, because of his perfected restorations and wide studies of the sea-serpent like saurians, the mosasaurs and other marine saurians, must rank as the highest



authority-. It is largely on his material that it is possible to present something like a complete view of the gigantic monsters that swam the Cretaceous seas and gave origin to our notions of mythical sea serpents. Kansas is the great center of the Cretaceous time of occupation, and it is within its borders that the largest number of species and genera of sea serpents have been discovered. It is natural, perhaps, that living in the vicinity of the most prolific Cretaceous remains, Professor Williston should be better able than scientists more remote to complete our knowledge of marine saurians.

There are three groups of the serpentlike sea saurians—the ichthyosaurs, plesiosaurs, and mosasaurs. Of the mosasaurs, Kansas has produced the largest number of species, twelve of which have been satisfactorily described. New Jersey, Alabama, Carolina, and Mississippi have perhaps ten valid species. Dakota has favored us with three species. It is estimated that of fifty species attributed to North America, about twenty-five or thirty will be distinguished as