AGE OF THE ARAPAHOE AND DENVER. 227 



of genera and specie- have been based on some of the best pree 

 specimens from the Denver Basin. A large number of the remains 

 belong, moreover, more or less distinctly, to dinosaurian forms which have 

 been discovered in much greater perfection in other localities within the 

 lasl few years, so thai a review < it' these other discoveries Is accessary in 

 discussing the geological importance of the fossils of the 1 >enver area. 



Of the vertebrates from the formations now under discussion the first 

 to he described by Professor Marsh was found in place in the Denver beds 

 near the Platte River, in Highlands. It was at firsl described as Bison 

 alticornis, and assumed by Professor Marsh to probably indicate a Pliocene 

 formation. 1 In 1889 this fossil was recognized by him as belonging to the 

 new family of horned dinosaurs, the Ceratopsidae, which he had mean- 

 time founded on specimens discovered in Montana." Other remains from 

 the Denver Basin were at this time referred to the same family, and in more 

 recent years, as various representatives of dinosaurian types have been 

 described from the collections made in Wyoming or Montana, some of the 

 less perfect hones of the Denver region have been referred to the new 

 species. Some other vertebrate forms have also been identified, and at 

 present the list of species known from the post-Laramie of the Denver 

 region is as follows: 



Arapahoe formation: 



Dinosaurs: Ceratops montanus. 



Triceratops aniens (type). 



Clao8auru8 annectens. 



Ceratops alticornis. 

 Denver formation : 



Dinosaurs: Ceratops alticornis (type). 



Ornithomimus velox (type). 



Tricera tops h or ridus. 



Claosaurus annectens. 

 Turtles: Compsemys victus. 

 Trionyx foveatus. 

 Crocodile: Crocodilus humilus. 

 Fish: Lepidotus occidentalis. 



1 Notice of new fossil mammals : Am. .lour. Sci., Vol. XXXIV, 1887, p. 323. 

 ''Anew family of horned Dinosauria from the Cretaceous: Am. .Jour. s< i., Vol. XXXVI, 1888, 

 p. 477. Notice of new American Oinosauria: Ibid., 188!(, p. 334. 



