1 84 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



into temporal ridges. No definite postorbital process is formed, but its 

 position is indicated by a small vascular foramen, which differs from that 

 of Nothrotherium in presenting laterally instead of dorsally. The nasal 

 suture is slightly concave, but there is no distinct nasal process. 



The nasals are narrow and moderately elongate, extending to the 

 anterior rim of the orbit, while in Nothrotherium they excavate the 

 frontals much more deeply and reach almost to the middle of the orbit. 

 These bones are moderately convex in both directions and anteriorly each 

 one is cut by a deep, narrow notch, forming thus a long, slender lateral 

 process, which accompanies the maxillary to the edge of the anterior 

 nares ; the median portion of each nasal is shorter and abruptly truncate 

 at the end, so that the sides of the narial opening extend considerably 

 farther forward than the roof, which is broadly emarginate. In Nothro- 

 therium, on the other hand, the medial portion of the nasal is the longer, 

 extending well beyond the maxillaries. The anterior nares are quite 

 small and rudely semicircular, though somewhat higher than wide. 



The premaxillaries are strikingly like those of Nothrotherium as fig- 

 ured by Reinhardt ('78, Tab. I, fig. 3) and are therefore very unlike those 

 of the other Pleistocene genera. Each of these bones is Y-shaped and 

 consists of three long and slender branches ; the anterior branch is very 

 unusually elongate, which sharply distinguishes this species from all the 

 other members of the genus ; it extends horizontally forward, ending in 

 a bluntly rounded point and is closely applied to its fellow of the opposite 

 side. Of the two posterior branches, the median one is simply a back- 

 ward continuation of the anterior branch and forms the premaxillary 

 spine, while the lateral branch curves strongly outward and articulates 

 with a shallow depression of the maxillary just in front of the first tooth. 

 The incisive foramina are relatively large, triangular openings, which 

 have an oblique position and are quite widely separated by the spines. 



The maxillaries are very large and the preorbital portion is relatively 

 shorter and higher than in Nothrotherium, but longer and lower than in 

 the other Pleistocene genera, and ends abruptly in front of the first tooth, 

 with a thin edge ; the alveolus of - forms quite a prominent, curved swelling 

 upon the side of the jaw and between this prominence and the orbit is a 

 deep fossa, which is a very conspicuous feature of the skull, when viewed 

 from above or below. The depth of this fossa varies much in the different 

 species of Hapalops, but is almost obsolete in Nothrotherium, in which 



