15 



as I rode through a valley washed out of this old ocean bed, I 

 saw no less than seven different skeletons of these monsters in 

 sight at once. The Mosasaurs were essentially swimming Liz- 

 ards, with four well developed paddles, and they had little affin- 

 ity with modern serpents, to which they have been compared. 

 The species are quite numerous, but they belong to compara- 

 tively few genera, of which Mosasaurus, Tylosaurus, Lestosaurus 

 and Udestosaurus, have alone been identified with certainty. The 

 genus Mosasaurus was first found in Europe. All the known 

 species of the group are Cretaceous. 



The Crocodilia are abundant in rocks of Cretaceous age in 

 America, and two distinct types are represented. The older 

 type, which is foreshadowed by Belodon of the Trias, has bicon- 

 cave vertebra?, and shows marked affinities with the genus 

 Teleosaurus, from the Jura of Europe. The best known 

 genus is Hyposaurus, of which there are several species, all 

 more or less resembling in form the modern Gavial of the 

 Ganges. A peculiar intermediate form is seen in Diplosaurus, 

 from the Wealden of the Rocky Mountains. The second type, 

 which now makes its appearance for the first time, has pro- 

 ccelian vertebras, and in other respects resembles existing Croc- 

 odiles. The genera described are Bottosaurus, Holops and Tho- 

 racosaurus, none of which, so far as known, pass above the 

 Cretaceous. Of Crocodilia with opisthocoelous vertebra?, Amer- 

 ica, so far as we know, has none. Specimens similar to those 

 so termed in Europe, are not uncommon here, but they per- 

 tain to Dinosaurs. 



In the Eocene fresh-water beds of the West, Crocodilians 

 are especially abundant, and all, with the exception of Limno- 

 saurus, belong apparently to the genus Crocodilus, although 

 some species show certain points of resemblance to existing 

 Alligators. The Miocene lake-basins of the same region 

 contain no remains of Crocodiles, so far as known, and the 

 Pliocene deposits have afforded only a single species. The 

 Tertiary marine beds of the Atlantic Coast contain com- 

 paratively few Crocodilian remains, and all are of modern 



