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In remains of reptiles and fishes the western Cretaceous formation abounds. 

 Many of these have been described by Professor Cope and Professor Marsh. 

 Among the reptiles are some of the largest and most wonderful of their kind, 

 represented by great turtles allied to Atlantochelys ; numerous species of 

 Mosasaurus and closely related genera ; the Polycotylus and the long-necked 

 Discosaurus allied to Plesiosaurus ; and Pterodactyls, with an enormous 

 expanse of wings. 



The following pages contain descriptions of remains of reptiles and fishes 

 which have come under the observation of the author mainly from the west- 

 ern Cretaceous deposits. A few of the remains are doubtful as to the forma- 

 tion from which they have been derived, but are believed to be Cretaceous 

 fossils. As intimately related with the western Cretaceous fossils, descrip- 

 tions of a few others are included from eastern localities. 



Most of the fossils were submitted to the examination of the author by the 

 Smithsonian Institution, and form part of a collection from the Smoky Hill 

 Piver, Kansas, and from the Indian Territory, presented to the Army Medical 

 Museum of Washington by Dr. George M. Sternberg, United States Army. 

 Others from the Smithsonian Institution were collected in the vicinity of 

 Fort McRae, New Mexico, and were presented to the Army Medical Museum 

 by Dr. W. B. Lyon, United States Army. Many of the fossils were collected 

 during the explorations of Professor Hayden. The remainder form part of 

 the Museum of the Academy of Natural Sciences and Swarthmore College, 

 or have been contributed by Dr. William Spillman, Dr. John L. Leconte, 

 Professor George H. Cooke, William M. Gabb, George H. Truman, and 

 others. 



REPTILES. 



Order Dinosauria. 

 POICILOPLEURON. 



POICILOPLEUEON VALENS. 



During Professor Hayden's expedition of 1869, a fossil was given to him 

 asa " petrified horse-hoof." The specimen was found in Middle Park, Col- 

 orado, and according to Professor Hayden was probably derived from a forma- 

 tion of Cretaceous age. Similar specimens were reported not to be uncommon, 

 and were known as above designated. Indeed the writer has seen a second 

 specimen, which was also called a fossil horse-hoof, but unfortunately his 

 notes in relation to it have been mislaid. 



