428 PATAGONIAN EXPEDITIONS: PAL/EONTOLOGY. 



MEASUREMENTS. 



Lower dentition, length 012 Lower incisor, thickness 0015 



" " " pi mi . . .005 Mandible, depth below p f 004 



Lower incisor, width 0005 



SCIAMYS LATIDENS Sp. HOV. 

 (Plate LXVII, Figs. 1-3.) 



The type of the species (Princeton collection, No. 15,944) is the most 

 complete individual of the genus yet obtained. It consists of the skull, 

 lacking the occiput and basis cranii, mandible, five cervical and several 

 thoracic vertebrae, the sacrum and the greater part of the manus, tibia, 

 fibula and pes. Collected by Messrs. Hatcher and Peterson at Killik 

 Aike. 



In skull and dentition S. latidens stands well apart from the other 

 species of the genus and forms a transition to Acaremys, to which it 

 would be referable, were it not for the character of the lower incisors. 

 The upper incisors are quite broad, in marked contrast to the slender, 

 delicate teeth found in most of the other species of Sciamys, and have 

 distinctly convex faces, as much so as in Acaremys murinus, while the 

 lower incisors are plane and are also broader than in the various preced- 

 ing species, from which they further differ in the presence of a raised 

 enamel border along the outer margin of the front face. The upper pre- 

 molar is somewhat reduced in size, making the difference between this 

 tooth and m 1 - unusually great, while n% is conspicuously smaller than in 

 the other species. 



The skull is characterized by the broad and heavy rostrum with nearly 

 parallel sides, and by the wide, nearly plane interorbital region ; the 

 frontals have distinct postorbital processes, a difference from the other 

 species ; the anterior border of the frontals is excavated in a broad, semi- 

 circular notch, to receive the nasals and premaxillae. The nasals, which 

 are rather short, are narrowest posteriorly, broadening gradually forward ; 

 their posterior half is nearly plane, the anterior portion moderately con- 

 vex. The antero-superior angle of the premaxilla, between the incisor 

 alveolus and the nasal, is very small, much smaller than in S. principals. 

 The palate is somewhat broader in front than behind, and the difference 

 is rather more marked than in the other species. 



The mandible does not exceed that of S. principals in length, but is 



