EXPLOBATIONS FOB FOSSIL VERTEBRATES. 565 



three-toed horses, including (1) those with excessively light, almost deer- 

 like limbs; (2) others with shorter, more robust limbs, less specialized 

 and leading apparently into the true modern horse; (3) others again, 

 forest living forms, with spreading side toes, perhaps designed to pre- 

 vent the animals from sinking into the soft ground of the swampy 

 regions which they may have inhabited. Here also was found the 

 complete skeleton of the camel, Camelus occidentalis, of mastodons, 

 and of several other new types of animals, especially the wolves and 

 foxes of the period. 



Another American Museum expedition worked its way into the 

 waterless desert in western South Dakota, where, in the bed of an 



Complete Mounted Skeleton op the Neohipparion ivhitneyi, A Three Tof.d Horse of 

 the Upper Miocene Epoch. In the Ameiican Museum of Natural History. 



ancient inlet of the sea, perhaps ten million years ago, were deposited 

 the skeletons of two well-known varieties of sea reptiles, mosasaurs and 

 plesiosaurs. These were found encased like mummies in a soft rock 

 imbedded in larger concretions which stood up like mushrooms in 

 what the westerners called a ' blow-out.' Numerous skeletons were 

 found in a beautiful state of preservation, and formed the chief feature 

 of this expedition. Just as Mr. Barnum Brown, the head of this party, 

 was on his way east, a telegraphic order directed him into northwestern 

 Arkansas to a comparatively recent deposit, perhaps 200,000 years of 

 age, made just prior to the glacial period. It recorded chiefly the small 

 western preglacial fauna, the field mice, shrews, minks, badgers, rabbits, 

 ancestors of familiar living western types, mingled, however, with re- 



