286 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 



tympanic process is very small, and the zygomatic process is short and 

 nearly straight, with a slight downward curvature ; the jugal, which is 

 missing, must have been unusually long. The lachrymal, which is of the 

 ordinary type, appears to be less prominent than in many other species, on 

 account of the breadth of the rostrum; in No. 15,163 the foramen is con- 

 siderably smaller than in the other skull, but the difference is probably 

 individual. The frontals have less of the hour-glass shape than usual, 

 owing to the shallowness of the postorbital constriction ; large sinuses 

 are indicated by the convexity of the forehead ; the sagittal crest is quite 

 distinct and bifurcates into well defined temporal ridges ; the spine which 

 overhangs the optic foramen is continued as a short ridge along the suture 

 with the orbito-sphenoid. The nasals are long and each one is convex 

 transversely, producing a groove along the median line ; they are nar- 

 rowest at the hinder end, broadening gradually to the anterior end, which 

 projects freely beyond the maxillaries ; the lateral notches are shallower 

 than \n-Hapalops and the lateral processes present outward instead of 

 dorsally, very much as in Mylodon. 



The premaxilla:; are missing, but the facets for them indicate that they 

 were of the type common to the Megalonychidce, with certain peculiarities ; 

 the facet for the postero-external branch is a high, narrow concavity, which 

 rises unusually far upon the sides of the anterior nares ; a second and 

 much smaller facet for the same branch is upon the lateral aspect of the 

 palatine process, while the median notch for the spines is not unlike that 

 of Hapalops, but somewhat smaller. The preorbital portion of the max- 

 illary is large and the fossa is of variable depth ; the zygomatic process is 

 not very prominent, but is broad antero-posteriorly and is perforated by a 

 relatively small infraorbital foramen. The hard palate is of the type 

 usual in the family, but is wider than in most of the genera and, owing 

 to the irregular sizes of the teeth, its width varies more in the different 

 parts ; the posterior convexity is moderate and extends only to the space 

 between ~ and - and in front of this the palate is flat, or slightly concave. 

 A distinct difference between the two specimens is in the shape of the 

 posterior narial opening; in No. 15,163 the front part of this opening is 

 narrow, with a median spine, and extends nearly to the anterior face of --, 

 while in 15,561, it ends behind A , has no spine and is broader. The 

 pterygoids are not entirely covered by the descending plates of the ali- 

 sphenoids ; in one of the skulls (No. 15,163) at the base of each pterygoid, 



