22O PATAGONIAN EXPEDITIONS: PAL/EONTOLOGY. 



The tympanic is a small, incomplete ring, with the usual very large 

 and irregular auditory meatus. The alisphenoid is quite large, especially 

 the descending process; dorsally, it articulates with the squamosal by 

 means of two distinct processes, separated by the large opening which 

 represents the combined foramina rotundum and ovale. The orbito- 

 sphenoid is small and has an irregular shape, its anterior border being 

 deeply notched by the optic foramen and somewhat below and behind 

 this by the foramen lacerum anterius. The parietals have about the same 

 proportions as in the other species of the genus, but there is much indi- 

 vidual variation in the degree of vaulting and in the consequent capacity 

 of the cerebral fossa. The squamosal, jugal and lachrymal display no 

 constant peculiarities. The frontals are characterized by their narrowness 

 and elongation and by the constant presence on their posterior half of a 

 sagittal crest, a low and thin ridge which is better developed in the older 

 specimens. The fronto-nasal suture is very variable ; usually it forms a 

 single transverse curve, with concavity forward, interrupted in the middle 

 by the very short median processes of the frontals, but sometimes these 

 processes are conspicuous and divide the suture into two well-defined 

 curves. 



The nasals are short, rather broad and flat, or slightly convex ; they are 

 broadest behind, where they may be separated by the median processes of 

 the frontals, and decidedly divergent; anteriorly, they have the usual 

 deep lateral notches, producing the long, slender processes which accom- 

 pany the maxillaries to the edge of the anterior nares ; the median portion 

 is broad and bluntly pointed. 



The premaxillaries have the shape common to all the species of Hap- 

 alops, but the anterior branch is much shorter than in H. longiceps or H. 

 indifferens, while the postero-external branch is broader and more de- 

 pressed ; the incisive foramina are narrow and slit-like. The maxillaries 

 extend for some distance in front of the first tooth as a thin facial plate ; 

 the preorbital fossae are distinct, but much more so in some individuals than 

 in others. The palate varies much in width, in the degree of its anterior 

 expansion and in convexity, no two individuals being alike in these re- 

 spects, as is also true of the anterior median notch of the palate for the 

 premaxillary spines, which is always broad and more or less U-shaped, 

 but varies much in depth. The posterior nares have the usual shape, 

 their side-walls curving downward in great, wing-like extensions of the 



