228 PROCEEDINGS OF THE ACADEMY OF [1892. 



the subsidiary tubercles which form the trefoils of the inner side of 

 the molars there are a few other tubercles closing the valleys. The 

 second true molars have a narrow fourth cross-crest. jNIeasurements : 

 Length of left ramus preserved 2.55 feet ; length from anterior 

 base of coronoid process to apex of snout 1'55 feet; length of sec- 

 ond true molar '45 feet ; Avidth between second molars "35 feet ; 

 total width of rami at middle of M. 3-l'4 feet; width of crown of 

 M. 3 at front crest '35 feet ; diameter of tusk near middle •625 feet. 

 This species is nearest to the Mastodon andmvi Laurill., but that 

 species, according to Burmeister, has an elongate symphysis, although 

 without tusks. 



Mastodon cfr. mirificus Leidy. 



Rather common. 

 Mastodon cfr. shepardii Leidy. 



One molar obtained. 



PERISSODACT^LA. 



Equus simplicidens Coi)e, 1. e. 



The most abundant mammal and retaining exactly the characters 

 of the molar teeth as originally defined. 



Equus, sp. 



Smaller and with plicate enamel. 



Equus, sp. 



Much smaller than the last, and quite rare ; not determined. 



ARTIODACTYLA. 



Pliauchenia. 



A large species about the size of the existing camel is abundant ; 

 not determined. PlimiGhenia bones of a species larger than the 

 last may be referable to this genus. Small Artiodactyla not 

 determined. 



Of the preceding list of fifteen species it may be remarked that 

 Megdlouyx and Equus are not Loup Fork genera, while Mastodon and 

 Pliauchenia are such. No species is found in the Loup Fork bed. 

 On the other hand, Megalonyx and Equus are Equus-bed genera, while 

 Pliauchenia and Mastodon have not been found in them, although 

 it is probable that the latter existed. No species is found in that 

 horizon. The conclusion is inevitable that the fauna of the Blanco 

 bed is intermediate between the two mentioned, and that it fills an 



