BY S. W. WILLISTON AND E. C. CASE.

PART I, CLIDASTES, WITH [PLATES II-VI].

The group of extinct Cretaceous reptiles known as the Mosasaurs or Pythonomorpha was defined by Cope, “to whom Science is so largely indebted for its present knowledge of this interesting order of reptiles” (Marsh), in 1869.[4] Although some of the characters assigned by him to the order have since been shown to be inapplicable, and the group to have less value, yet his name, Pythonomorpha, has been generally retained. Lydekker and Zittel have assigned to the group a subordinal value, as has also Marsh, though under a different name. Owen rejected it entirely, and Baur, more recently,[5] has united it with the Varanidae to form a super-family, as follows:

The group, whatever may be its rank or position, includes, so far, the following genera: Mosasaurus Conyb., Liodon Owen, Platecarpus Cope, Clidastes Cope, Baptosaurus Marsh, Sironectes Cope, Plioplatecarpus Dollo and Hainosaurus Dollo. Pterycollasaurus Dollo, founded upon Mosasaurus maximilianus Goldf., is omitted as doubtful. All of these genera, save Plioplatecarpus and Hainosaurus, have been recorded from North America, Clidastes, Baptosaurus and Sironectes being peculiar to this country. Of these latter three genera, however, Clidastes alone is well known; but this genus is suspected by Lydekker of being the same as the imperfectly known European Geosaurus Cuvier. Thus it seems that the genera, or at least the most of them, have a wide distribution; Platecarpus, in fact, is said to occur in New Zealand.

In America, members of the group have been discovered in the Cretaceous deposits of New Jersey, Alabama, North Carolina, the upper Missouri region, Nebraska, Kansas and New Mexico. Probably nineteen-twentieths of all the known specimens, however, have been obtained in western Kansas. The material now in the University Museum, all from Kansas, comprises several hundred specimens of these animals, including, probably, the best ones known. It is upon this material that the following preliminary studies are chiefly based.

The genus Clidastes, as first described by Cope, was based upon two dorsal vertebrae of C. iguanavus, the type species, from New Jersey. Shortly afterward, however, he gave a full and careful generic description, as derived from an unusually good specimen of an allied species, C. propython, from Alabama. Only a little later, Marsh described a genus, which he called Edestosaurus, from Kansas, but without giving any real, distinctive differences from Clidastes, following the very reprehensible practice of naming supposed new forms in the hopes that future distinctive characters might be found. The genus Edestosaurus has been rejected by nearly all save the authors of the American text-books in Geology. It seems hardly necessary to point out the identity. The only distinctive character the author gave for his genus was the insertion of the pterygoid teeth, and even this character he modified later—“Palatine (sic) teeth more or less pleurodont.”[6]

This character, even were it real, is of very slight value; indeed it cannot be used to distinguish the species even.