406 PATAGONIAN EXPEDITIONS : PALEONTOLOGY. 



Loncheres, but is more elongate, with narrower and less tapering cranium 

 and somewhat broader rostrum than in the latter. There is no sagittal 

 crest, but on the hinder half of the parietals is a short, narrow and ob- 

 scurely marked sagittal area, which in front suddenly expands to the full 

 width of the cranium, its borders becoming confluent with the supraorbital 

 ridges. The coronal suture is not so straight as in the modern genera, 

 but is slightly curved, with concavity forward. The supraorbital border 

 is quite as prominent as in the recent genera and has a well defined post- 

 orbital process not present in the latter. The frontals are nearly flat, 

 except anteriorly, when they show a pair of inconspicuous swellings pro- 

 duced by the sinuses. The nasals are relatively quite large and of some- 

 what foliate shape, broadening and becoming very convex anteriorly, where 

 they are curved down on the sides of the rostrum ; posteriorly, they notch 

 the frontals more deeply than in the modern genera. The premaxillaries 

 are much as in Loncheres and the anterior border, in front of the incisor 

 alveoli, forms a similar sharp vertical keel, but the incisive foramina are 

 considerably larger and the ascending rami, which extend to the frontals, 

 are broader. The posterior nares and hard palate resemble those of 

 Echimys, but the palate is rather more triangular, owing to the slight 

 anterior convergence of the two dental series. 



The mandible differs from that of Echimys and Loncheres in a number 

 of particulars. The ascending ramus is set farther back, so that n% is but 

 partly concealed when the jaw is viewed from the side, while in the recent 

 genera this tooth is entirely hidden ; the coronoid process, though small, 

 is much less reduced than in the two recent genera, and the sigmoid notch 

 is correspondingly deeper ; the masseteric crest, which pursues a similar 

 course, is less prominent and does not extend so far forward ; the ante- 

 rior part of the horizontal ramus is less inclined ventrally. 



Specimens of Stic homy s are not at all uncommon and the genus is rep- 

 resented in the Santa Cruz beds by a considerable number of species, 

 which differ markedly in size. However, as these species have all been 

 established upon jaws, better material may well modify the results. 



STICHOMYS REGULARIS Ameghino. 



(Plate LXV, Figs. 17-19.) 



Stichomys regularis Amegh. ; Enumeracion sistem., etc. ; 1887, p. 10. 

 The typical species is of moderate size and has a narrow, tapering 



