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 subdivision 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.
ART. XXI.-ffi)tice if G£g(J;ntic lforned Din08Ct'uJ'ia fl'om the OretcWeOtl8; by Professor O. C. MARSH. TilE remarkable reptiles which the writer recently described, and placed in a new family, the Oeratop8idm, * prove to be more and more wonderful as additional specimens are brought to light. There appear to he two or three genera, and several well-inarked species, already discovered, and the object of the present paper is to notice briefly some of their characteristic features so far as investigated. Tl'icemtop8 hOl'l'id'l£8, gen. nov. The animal described by the wI'iter as Oel'(ttop8 1"orrhbl8t possesses some remarkable characters not before known in the J)'/:no8ClItr1:lt. In addition to the pnir of massive horn-cores on
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