280 PATAGONIAN EXPEDITIONS I PALEONTOLOGY. 



sively exposed on the surface of the occiput between the exoccipital and 

 squamosal and forms a prominent ridge with a deep and narrow fossa on 

 each side of it ; in the outer one of these fossae is a large venous foramen ; 

 ventrally the periotic ends in a large, subcylindrical mastoid process, with 

 a cup-shaped surface for the stylo-hyal. The parietals are large and form 

 nearly the whole cerebral roof, with prominent sagittal crest extending 

 along their entire length. The squamosal is also large and extends to the 

 occipital surface, making up nearly half of the occipital crest ; ventrally 

 this crest ends in a prominent tubercle, which is smaller than in M. jeffer- 

 soni and nearer to the mastoid process ; the zygomatic process is much 

 like that of Hapahps and pursues a horizontal course, not curving down- 

 ward, nor diverging so far from the side of the skull as in Megalonyx ; 

 another difference from the latter is that the dorsal border of the zygoma 

 does not become continuous with the occipital crest. 



The temporal ridges of the frontals are much less prominent than in 

 the Pleistocene species and the postorbital processes seem to have been 

 insignificant ; the frontal sinuses are much less prominent and the fore- 

 head is but moderately convex. The lachrymal resembles that of the 

 other Santa Cruz Gravigrada and is far more prominent than in Mega- 

 lonyx. The nasals are short, unusually broad, moderately curved longi- 

 tudinally and almost plane transversely. The anterior nares are quite 

 large and considerably higher than they are wide ; in shape they are much 

 as in the Pleistocene species, but are covered more by the nasals and less 

 by the maxillaries. 



The premaxillae have been lost, but from the facets on the maxillaries 

 and the smaller, more V-shaped notch of the anterior border of the palate, 

 it may be inferred that they were longer and more slender than in Mega- 

 lonyx. The maxillary is longer than in the latter, especially the preorbital 

 portion, with much better defined preorbital fossa and far more prominent 

 zygomatic process ; the hard palate is very rugose and is perforated by 

 many venous foramina, but the region between the molariform teeth is 

 less convex than in many Santa Cruz species and conspicuously less so 

 than in M. jeffersoni. The posterior nares have a shape similar to that 

 of the latter, but differ in the wide separation, dorsally, of the pterygoids, 

 which, in the Pleistocene species, meet in the median line and conceal the 

 presphenoid and part of the basisphenoid. Part of the vomer is visible, 

 descending gradually forward into the nasal chamber. 



