G. GENERAL NATURAL HISTORY AND ZOOLOGY. 305 



G. GENERAL NATURAL HISTORY AND ZOOLOGY. 



ORIGIN OF ANIMAL FORMS. 



Professor Cope in an essay published by the Hayden 

 United States Geological Survey, dated February, 1874, dis- 

 cusses the origin of the great population of animal forms 

 which previous explorations had disclosed in the lake de- 

 posits of Wyoming. His conclusion was that they had been 

 derived by migration from the South, as geological investi- 

 gations pointed to the earlier elevation of the land in that 

 direction. During the summer of 1874, Professor Cope, as 

 paleontologist of the United States Survey under Lieutenant 

 Wheeler, sought for and discovered in New Mexico a great 

 mass of lacustrine deposits, of somewhat earlier age than 

 those of Wyoming, and containing the remains of a great 

 number of animal species and genera, which so nearly re- 

 semble those of Wyoming as to leave no doubt that the lat- 

 ter were derived by descent and migration from New Mexico 

 and the South. 



In a memoir read before the Academy of Natural Sciences of 

 Philadelphia at nearly the same time, the same writer states 

 that the primitive type of the mammals with convoluted 

 brains " must have been bunodonts with pentadactyle plan- 

 tigrade feet ;" that is, must have had tubercle-bearing grind- 

 ers and five -toed feet, whose entire soles were applied to 

 the ground in walking, and not merely the toes, as in most 

 living animals. It was also stated that variations in the 

 number and relations of the front teeth might be expected 

 in such a hypothetical group of animals, which was named 

 BiinotheriidcB. During the explorations in New Mexico the 

 following season a remarkable genus was discovered, and 

 afterward named Calamodon. Its jaws and teeth were ob- 

 tained, and the latter had tubercle-bearing crowns. Subse- 

 quently Professor Marsh described more perfect specimens, 

 which show that this animal was also five-toed (pentadactyle), 

 and walked on its soles (plantigrade). With other similar 

 genera he forms an order Tillodontia, and says that they 

 are related to hoofed animals {JIngulatci) and Carnivora, and 



