394 PATAGONIAN EXPEDITIONS I PALEONTOLOGY. 



those of the last named genus in shape, but are lower and wider. The 

 premaxillaries are shorter than in Myocastor or Capromys and their ven- 

 tral edentulous surface is broader ; the long, narrow, incisive foramina are 

 more as in the latter genus ; the frontal processes are longer and narrower 

 than in either. 



The maxillaries are lower vertically than in Myocastor, in correlation 

 with the less completely hypsodont teeth ; the infraorbital foramen is lower 

 and wider, and of quite a different shape, and has no groove for the nerve ; 

 the preorbital fossa is much more deeply impressed, as in Dasyprocta, an- 

 other resemblance to which is the large size of the lachrymo-nasal open- 

 ing. The bony palate is considerably wider than in Myocastor, especially 

 at the anterior end, the two series of upper teeth converging less forward. 

 The palatines are longer, extending forward to the middle of m 1 , and the 

 posterior palatine foramina notch the palatines more deeply, so as to be 

 almost entirely enclosed in them. The posterior nares are narrower and 

 more elongate than in Myocastor, extending almost to the middle of m 1 , 

 with a short, sharp, median spine on the anterior border. The pterygoids 

 are not well preserved in any of the specimens, but apparently the fossa 

 did not communicate with the orbit; it is, however, connected with the 

 posterior nares by a round aperture, bounded ventrally by an extension of 

 the pterygoid, which joins the bulla, somewhat as in Dasyprocta. 



The mandible is very different from that of Myocastor and might be 

 described as intermediate in character between that of Capromys and that 

 of Dasyprocta. The horizontal ramus is short and heavy ; the masseteric 

 ridge is quite well developed, but is less prominent than in Myocastor or 

 Capromys; on the other hand, the pterygoid ridge is much more promi- 

 nent than in Dasyprocta, making the ventral border of the angle much 

 wider; in none of the specimens is the angular process complete, but it 

 would appear to have been shorter than in any of the three recent genera 

 named. The coronoid process, which in Myocastor has almost disap- 

 peared, is much higher than in the other two genera mentioned, rising as 

 high as the condyle, from which it is separated by a deep and narrow 

 sigmoid notch; the process is also quite broad, especially at the free end; 

 at the base of the coronoid is a small, but well defined, masseteric fossa ; 

 the condyle is large and convex, in shape quite like that of Myocastor, but 

 a resemblance to Dasyprocta may be seen in the thin, plate-like extension 

 behind the condyle, though this extension is considerably shorter and has 



