826 



ON THE EXTINCT MAMMALIA OP 



Additional remahis of equine animals from Little White River, or the South Forh of the 

 main stream of Maldsi-ta Walcjpa, or White River, 



The collection of Prof. Playden, obtained in his expedition in the summer of 1866 

 at Dakota, contains a number of remains of equine animals, which were found in 

 association with a few others of Procamelus occidenialis, Merycodus necatus, etc. They 

 were discovered on Little White River, in loose sand belonging to the same formation 

 as that on the Niobrara River, which has yielded such an abundance of similar fossils. 

 Unfortunately the specimens throw no further light on the determination of the spe- 

 cies I have attempted to characterize in the preceding pages. The more important 

 ones are as follow : 



1. A pair of upper molars, contained together in a fragment of the jaw. They are 

 apparently the second and third of the series, belong to the left side, and are repre- 

 sented in figure 2, plate XXVII. The teeth more nearly resemble those of Ilippa- 

 rion occidentale, from White River, represented in figures 1 — 5, plate XYIII, on 

 which the species was originally characterized, than any of those subsequently de- 

 scribed from the Niobrara River or other locality. They are nearly alike in size and 

 complexity of arrangement of the enamel, but the internal median column of the 

 crown is proportionately somewhat narrower. 



The measurements of the teeth are as follow : 



Lines. 



. 19 



Length of crown of second molar externally. 



12J 



12J 



21 



12 



12 



Breadth of triturating surface, 

 Width of triturating surface. 

 Length of crown of third molar, 

 Breadth of triturating surface, 

 Width of triturating surface, 



2. An isolated superior molar, apparently a fifth of the series. It has nearly the 

 size, proportions and structure of the corresponding tooth of H. occidentale, repre- 

 sented in figure 1, plate XVIII, except that the inner median column of the crown 

 is rather narrower. Its measurements are as follow : 



Lines. 



Length externally at the middle, . . . . . .15 



Breadth, ......... lOJ 



Width (transversely), . . . . . . .Hi 



Breadth of internal column, . . . . . . 3J 



3. Three isolated molars, from intermediate positions in the series, resembling in 

 size,' proportions and structure those referred to Hipparion gratum, and represented in 

 figures 25 — 30, plate XVIII. Their measurements are as follow : 



