264 PATAGONIAN EXPEDITIONS '. PALAEONTOLOGY. 



are quite long and broaden anteriorly, where they are curved downward 

 at the sides and abruptly truncated, except that each has a broad and 

 very shallow notch, entirely different from the deep and narrow lateral 

 notches of Hapalops. The premaxillae are short, broad behind, narrow- 

 ing forward and ending in a blunt point; together they form a broad, 

 heavy, triangular and almost solid plate of bone, the incisive foramina 

 being reduced to narrow slits. The premaxillary facets on the maxillaries 

 are equally characteristic; that for the postero-external branch occupies 

 nearly the entire width of each maxillary, while the median notch of the 

 palate which receives the premaxillary spines is very narrow and shallow, 

 quite unlike that seen in any other genus. The zygomatic arch does not 

 differ in any important respect from that of Hapalops and the jugal, with 

 its long suborbital process, is quite as in that genus. 



The mandible has a rather elongate horizontal ramus, the ventral 

 border of which is but slightly convex, in marked distinction from that of 

 Hapalops, and the concavity beneath the ascending ramus is correspond- 

 ingly slight. The symphysis is short and the profile of the chin is thus 

 quite steep ; nevertheless, the predental beak is quite elongate and con- 

 tracts anteriorly to a rounded edge, which is notched in the median line. 



MEASUREMENTS. 



Skull, median basal length, including Palate, width at ^ 017 



premaxillary .200 " " " &- 014 



" " " excluding Mandible, length of predental beak 040 



premaxillary .186 " depth below ^ 036 



Palate, width at 1 025 thickness below 3 029 



HYPERLEPTUS SECTUS Ameghino. 



Hyperleptiis sectus Amegh.; Rev. Argent, de Hist. Nat, T. I, 1891, p. 155. 



This species is closely allied to the preceding one and may prove to be 

 identical with it. It is distinguished by the form of the last upper tooth, 

 , which is transverse and not subcylindrical, and by the much more 

 decided constriction of the palate. The very broad muzzle, with its pro- 

 jecting caniniform teeth, emphasizes the likeness to Rucholccops. The 

 premaxillaries are not known, but the facets for them upon the maxillaries 

 are quite as in H. garzonianus. 



The following measurements are from the type-specimen in the 

 Ameghino collection. 



