392 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



in the fossil, and the teeth of Agouti, especially the lower molars, might 

 readily be derived from the Neoreomys type. 



Skull (Plate LXIV, fig. 6). The skull is more like that of Capromys 

 than that of Myocastor, though with many resemblances to that of 

 Dasyprocta. In general proportions and appearance, this skull might be 

 described as intermediate between Capromys and Dasyprocta ; the peculi- 

 arities of the Myocastor skull are not foreshadowed in Neoreomys. As a 

 whole, the skull is long and narrow, much as in Capromys ; compared 

 with that of Dasyprocta, the cranium is relatively longer, the orbit con- 

 spicuously smaller, and the rostrum shorter, lower and less tapering. 

 The proportionate lengths of the parietal and frontal zones are much as in 

 Capromys, but there is a short and well defined sagittal crest on the 

 hinder half of the parietals. 



The occiput (Plate LXIV, fig. 6 C ) is not unlike that of Myocastor, aside 

 from the altogether exceptional character of the paroccipital and mastoid 

 processes in the latter; it is low and wide, slightly concave and with 

 distinct median ridge; the foramen magnum is high and narrow, as in 

 Myocastor, differing from Capromys and Dasyprocta, in which the prin- 

 cipal diameter is transverse ; the paroccipital processes have about the 

 same relative development as in the last-named genus, but are more 

 closely applied to the large tympanic bullse. The supraoccipital is ex- 

 tended much farther upon the roof of the cranium than in Myocastor or 

 Capromys and differs notably from these genera in having no lateral pro- 

 cesses, and not extending down over the periotic, from which it is sepa- 

 rated by the supramastoid process of the squamosal. The tympanic and 

 periotic are not unlike those of Dasyprocta, but have a still closer resem- 

 blance to those of Cavia; the periotic is quite extensively exposed on the 

 side of the cranium, but the ascending process is narrower and the mastoid 

 process is hardly more distinct than in the latter genus. The tympanic is 

 inflated into a large bulla and coossified with the periotic ; the auditory 

 meatus is a short, incomplete tube, with ventral slit opening into the 

 central hole in the outer wall of the bulla almost exactly as in Dolichotis. 



The squamosal differs in several particulars from that of Myocastor ; 

 anteriorly, it does not extend so far along the frontals, being more as in 

 Capromys in this respect, while the supramastoid process, is considerably 

 broader than in either of the genera named. The zygomatic process most 

 resembles that of Myocastor, but extends less outward and more down- 



