410 0. G. Marsh — Description of Miocene Mammalia. 



The tooth represented in figure 3 is the last right molar, 

 and was found at the same locality under circumstances which 

 render it probable that it may have pertained to the same 

 animal. The premolar agrees closely in form with the cor- 

 responding tooth in Elotherium, but the last lower molar, 

 shown in figure 3, has, in addition to the four cones character- 

 istic of Elotherium, a distinct fifth posterior cone, or heel, not 

 present in typical specimens of that genus. The two genera 

 represent a distinct family, which may be called the Elothe?'idce. 



Ammodon (Elotherhtm) bathrodon* 

 The type of the present species is the tooth shown on 

 Plate IX, figure 4. It is the last lower molar of the right 

 side, and, in its main features, agrees with the corresponding 

 tooth last described. It indicates an animal somewhat smaller, 

 but far exceeding in size most members of the group. Since 

 this type specimen was described, two or three skulls of the 

 same species have been secured by the writer, all found in the 

 Miocene of Dakota, in the same general region where the type 

 was discovered. These skulls agree in their general features 

 with that of Elotherium figured on Plate YIII, but the brain- 

 case is proportionately larger, and the processes on the lower 

 jaw are still more developed. The dependent angle of the 

 lower jaw slopes backward, and not forward as in Elotherium 

 crassum. The lower molar teeth, also, all have a posterior 

 lobe more or less developed, and the last lower molar has a 

 distinct heel. In one of these skulls, the space occupied by 

 the upper premolar and molar teeth is twelve inches, and the 

 space across the palate between the true molars is two and 

 one-half inches. 



Ammodon potens, sp. nov. 

 The present species is somewhat smaller than the one last 

 described, and differs in having a proportionately more elongate 

 skull and less robust teeth, especially in the molar series. All 

 the lower true molars have a distinct posterior cone, and this is 

 nearly as well developed on the first and second molars as on 

 the last. The processes on the lower jaw are more elongate 

 than in any other species of the group. The dependent 

 process on the malar is also especially elongate. The space 

 occupied by the lower premolar and molar series is twelve 

 inches, and by the premolars alone seven and one-half inches. 

 The depth of the lower jaw from the base of the canine to 

 the end of the process below is seven and one-half inches, and 

 the distance from the top of the fourth premolar to the end 

 of the middle process below is seven inches. 



The type specimen of the present species is from the Miocene 

 of Colorado. 



* t This Journal, vol. vii, p. 534, May, 1874. 



