CEETACEOUS VERTEBRATE FOSSILS. 509 



been found on the eastern side of the mountains, but on the western slope, 

 and especially near Lake ( !omo, a large number have Keen discovered, and 

 described by the writer. In figs. 68, 69, and 70, on the opposite page, 

 are shown the lower jaws of three of these small mammals, all from 

 different localities in this horizon. 



In the Atlantosaurus beds east and west of the mountains various 

 invertebrate fossils have been found, but they are apparently all of fresh- 

 water species, and hence of little value as evidence of geological age. The 

 most abundant of these are ruins, and a typical locality is on Oil ('reek, 

 north of Canyon, just above the well-known strata containing vertebrate 

 fossils. Remains of plants also occur in this horizon, but those yet found 

 throw no light on the problem of age, which the characteristic vertebrate 

 fossils have fully determined. 



PAET III. 



CRETACEOUS VERTEBRATE FOSSILS. 



PTEKANODONTIA. 



PTERANODON. 



The next horizon in this region that contains important vertebrate 

 remains is known as the Pteranodon beds, and its general position is shown 

 in the section, fig. 23, where the characteristic genera found in these 

 strata are also recorded. The gigantic toothless pterodactyls belonging 

 to the order P.teranodontia are of special interest, and the skull of the 

 typical genus, Pteranodon, is represented below in figs. 71 to 74. 



These huge flying reptiles, when alive, had a spread of wing of from 

 1") to 25 feet, and their remains are now quite abundant in the chalk 

 deposits of this horizon, especially in Kansas. With them are found the 

 remarkable birds with teeth, of the genera Besperornis and Ichthyornis 

 (PI. XXVI), described by the writer. In the same strata the remains of 

 the mosasaurs are the most numerous of all the vertebrate fossils there 

 entombed, while plesiosaurs and turtles are also represented, and fossil 

 fishes are especially abundant. 



DINOSAURS. 



I T.liATOI'Klll.K. 



The next horizon rich in vertebrate fossils is the Ceratops beds, so 

 named by the writer from the gigantic horned dinosaurs thai are especially 



