54 ON THE EXTINCT MAMMALIA OF 



of fossils from the Mauvaises Terres of White River, Dakota, there are also remains 

 indicating a species of Drepanodon smaller than our existing Panther, Felis concolor. 

 Bronn, in the Lethiea Geognostica, has divided the various described species of 

 Drepanodon into three groups, as follows : 



Drepanodon, characterized by having the canines entire or without serrulation, 

 and the first lower premolar with a trilobate crown and double fang. 



Machairodus, with the acute edges of the canines serrulate, and the first lower 

 premolar as in the preceding case. 



Smilodon, with the canines serrulate, and with the first lower molar with a simple 

 crown and single fang. 



The Dakota Drepanodon belongs to the second group, or that of Machairodus. 



Drepanodon prim^vus. 



Of the Dakota Sabre-toothed Tiger, previously described under the name of 

 Machairodus primaiviis, I have had the opportunity of examining four nearly com- 

 plete skulls and small fragments of several others. One of the specimens is described 

 and figured in the Ancient Fauna of Nebraska ; two are represented in figures 1, 5, 

 plate IV, as well as parts of a fourth in figures 2, 3, 4, of the same plate. 



The skull of D. primaiviis varies in size and in its details of form, though not to a 

 greater extent than in different individuals of the Panther. 



The face is proportionately longer and shallower, and the cranium shorter and 

 deeper than in the latter animal. 



Lateral view of the skull. — The upper outline of the skull has nearly the same 

 antero-posterior convex form as in the Panther, but the slope of the face, or of the fore- 

 head and snout together, is longer and straighter, and that of the cranium is shorter. 

 The front of the snout is more sloping, arising from a greater degree of prominence of 

 the alveolar portion of the premaxillaries. The chin is more vertical and deeper. 

 The temporal fossa rises upon an equally high but shorter sagittal crest, and extends 

 upon an equally prominent border separating it from the inion. 



The zygoma encloses a more contracted or narrower space than in the Panther. 

 Its posterior root has a deeper origin from the cranium, and descends more in its 

 outward course. Its anterior root below the orbit is shallow and thick, while the 

 masseteric impression is inferior and inconspicuous, in comparison with that of the 

 Panther. 



The temporal surface is less convex than in the latter animal, and upon the root of 

 the zygomatic process is less horizontal or more sloping. A large vascular foramen 

 pierces the back part of the parietal bone. 



