H. F. shorn — Mammalia in North America. 461 



variations in the crowns of the molar teeth in compensation 

 for the backward evolution of its feet. Scott has been espe- 

 cially investigating the upper Miocene horses ; I quote from 

 the MSS. he has kindly lent me, in which he proposes to re- 

 move also the classical Anchitherium of Cuvier. He says : 

 " These American genera, Mesohippus and Miohippus may 

 confidently be regarded as important members of the equine 

 stem, while Anchitherium (of Europe) from present informa- 

 tion would appear to belong to an abortive side branch leading 

 to no permanent results." Scott has also discovered an im- 

 portant intermediate form linking Miohippus with Proto- 

 hippus. 



The Palseotheres have not been found in America. 



The Tapir line has been traced by Cope and myself back to 

 Systemodon of the Wahsatch, and Isectolophus of the Bridger 

 and Uinta. These forms have simple premolars, but bear the 

 most striking resemblance to the Tapirs in the molars both 

 above and below. All previous attempts to determine the 

 Miocene representatives of the Tapirs have been erroneous. 

 Wortman and Earle have just published an account of two 

 lower Miocene species of true Tapirs, which, both in foot and 

 tooth structure, definitely carry the American Tapir line up to 

 the middle Miocene, where it is again lost sight of. These 

 species belong to the genus Protapirus, which Filhol has found 

 in the Oligocene of France, thus adding an important geologi- 

 cal parallel. The Wahsatch Tapirs were a little larger than 

 the Horses or Hyracotheres which were about the size of a 

 fox, and much smaller than the ancestral Titanotheres. 



Another family of small, slender perissodactyls more nearly 

 allied to the Lophiodons of Europe than any other American 

 forms are the Helaletidse, distinguished by feet tending to 

 monodactylism, and narrow hoofs like those of the deer ; even 

 in the Wahsatch Heptodon the lateral toes are quite short and 

 raised off the ground. The molars, like those of the lophio- 

 dons of Europe, are intermediate between those of the Tapir 

 and the Rhinoceros, but both teeth and feet preclude our unit- 

 ing these forms either with the Tapirs or with the Hyrachyus 

 family, as Cope has done. The Bridger successor is Helaletes, 

 which Marsh mistakenly supposed was an ancestral Tapir, and 

 the integrity of this line is now firmly established by the dis- 

 covery of the Miocene Colodon. This is described by Marsh 

 as a successor of Helaletes, and Wortman and Earle have just 

 published an account of the teeth and feet, showing that Colo- 

 don is widely separated from the contemporary true Tapirs, 

 and is the last member of the Heptodon-Helaletes line. 



The Rhinoceroses of America comprised the true Acera- 

 theriinae and Diceratheriinse, and what may be called the 



Am. Jour. Sci.— Third Series, Vol. XLVT, No. 276.— Dec, 1893. 

 32 



