124 EXTINCT AND VANISHING MAMMALS 



these latter and may have survived up till relatively recent 

 times. They are believed to represent genera closely akin to 

 the agoutis of South and Central America but present certain 

 differences in cranial and dental characters. They are in- 

 cluded here for the sake of completeness. 



Both were perhaps slightly smaller than the typical agouti 

 of Trinidad or Brazil, representing the genus Dasyprocta. 

 Anthony (1916, 1918) describes Heteropsomys as having a 

 skull smaller than that of an agouti, with a total length of about 

 70 mm. There are four molars in each jaw, of nearly equal 

 size, each with a prominent infolding of enamel on the middle 

 of the inner side in the upper teeth and on the outer side in 

 the lower teeth. In the few known specimens there are three 

 small transverse islands of enamel in the first upper tooth, 

 and two in the second (and probably two succeeding true 

 molars). An unworn tooth would doubtless show that these 

 are the result of wearing away the summits of shallow trans- 

 verse depressions in the enamel covering. The molars are each 

 provided with two short conical roots. The posterior narial 

 passage or interpterygoid fossa extends forward in a V-shape 

 to the level of the second molar. In general the skull is less 

 elongate and relatively wider than in typical agoutis. Anthony 

 writes that judged from the position of the remains discovered 

 "this rodent is doubtless of a later age" than either the small 

 ground sloth Acratocnus or the large rodent Elasmodontomys 

 found in the same cave deposits. 



Concerning Homopsomys, only a few broken crania are 

 known from which to determine its relationships. The denti- 

 tion is missing from these, except for a few fragments, but the 

 skull shows a similar broad, flattened, frontal area, with 

 bluntly pointed postorbital projections. In his later paper 

 Anthony (1918) writes: "Homopsomys is very closely related 

 to Heteropsomys. Indeed it now appears that the two forms 

 are probably congeneric, and I would make them so but for 

 the fact that the material at hand is rather inadequate." The 

 differences between the two, such as the length of palate, 

 smaller size of Heteropsomys, its lighter incisors, and more 

 convex frontals, may be characters due to age rather than 

 specific or generic characters, so that future specimens, if 

 obtained, may throw additional light on the relationship of 

 the supposed species. Although Miller compares his Brotomys 



