2 ODONTORNITHES. 



Along the eastern slope of the Rocky Mountains, and especially on the 

 adjoining plains in Kansas and Colorado, there is a series of Cretaceous 

 strata remarkably rich in vertebrate fossils. The deposits are all marine, 

 and, away from the mountains, they lie nearly horizontal. They have 

 suffered much from erosion, and are still wasting away, especially along 

 the river valleys. These beds consist mainly of a fine yellow chalk and 

 calcareous shale, both admirably adapted to preserve delicate specimens, 

 and here have been found the extinct Birds which form the subject of 

 the present memoir. 



The geological horizon of the known Odontornitlies is in the Middle 

 Cretaceous, and corresponds to the strata named by the writer the 

 " Pteranodon beds." The latter are included in sub-division number three, 

 in Meek and Hayden's section. The accompanying fossils are Mosasauroid 

 reptiles, which are very abundant ; Plesiosaurs, allied to Pliosaurus ; 

 Pterodactyles, of the genus Pteranodon; and many Fishes. With these 

 occur Rndistes, and occasionally Ammonites, Belemnites, and various 

 other Cretaceous invertebrates. 



The first Bird fossil discovered in this region was the lower end of the ■ 

 tibia of Hesperomis, found by the writer in December, 1870, near the 

 Smoky Hill River in Western Kansas. Specimens belonging to another 

 genus of the Odontornitlies were discovered on the same expedition. The 

 extreme cold, and danger from hostile Indians, rendered a careful explora- 

 tion at that time impossible. 



In June of the following year, the writer again visited the same 

 region, with a larger party, and a stronger escort of United States troops, 

 and was rewarded by the discovery of the skeleton which forms the type 

 of JSesperornis regalis, Marsh. Various other remains of Odontornitlies were 

 secured, and have since been described by the writer. Although the fossils 

 obtained during two months of exploration were important, the results 

 of this trip did not equal Our expectations, owing in part to the extreme 

 heat (110° to 120° Fahrenheit, in the shade) which, causing sunstroke and 

 fever, weakened and discouraged guides and explorers alike. 



