244 PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



the specimens this tooth has the usual bevelled crown, but in the third 

 (No. 9,293) we find a very interesting difference, at least on the right side, 

 the crown of the left side being broken ; in the specimen in question the 

 tooth is not bevelled and caniniform, but transversely grooved, like the 

 molariform teeth. This is the only known instance of the kind among the 

 Santa Cruz Gravigrada and is doubtless an individual abnormality, but it 

 is of interest as showing how readily the caniniform may be changed into 

 a molariform tooth, as has occurred, for example, in Megatherium. The 

 diastema is of varying length, though always quite short, and the molari- 

 form teeth are transversely rectangular ; - is quite small, - and - con- 

 siderably larger, and & very small. 



MEASUREMENTS. 



Type. No. 9,293. No. 9,250. 



Upper dentition, length 043 .041 .040 



" " 1-i 029 .027 .027 



1, length (i. e., antero-posterior diameter) 005 .005 .005 



" width (i. e., transverse diameter) O35 -003 .004 



1, length 005 .005 .005 $ 



" width 006 .007 .007 



3-, length 006 .006 .0063 



" width 008 .0085 .008 



, length 006 .006 .006 



" width 0075 .008 -0075 



i, length 003 .004 .0035 



" width 007 .006 .0065 



The skull (Plates XXXVII, figs. 4, 6; XXXVIII, 4, 6; XXXIX, 4, 

 4", 6, 6 a .) has much the same general appearance as that of//, elongatus, 

 but besides being smaller, differs in a number of details. The occiput is 

 low and the cranium is moderately arched upward to the parietal eminence ; 

 the brain-case is full and broad, but the postorbital constriction is not 

 very conspicuous, owing to the very moderate expansion of the forehead, 

 which is but slightly convex. No sagittal crest is present, but a faintly 

 marked sagittal area may be traced over nearly the entire length of the 

 cranium ; the area is narrowest in the frontal region, expanding pos- 

 teriorly, and in one of the skulls (No. 9,250) its hinder margin curves 

 downward and then forward, becoming continuous with the dorsal border 

 of the zygomatic arch and thus demarcating the area of the temporal fossa 

 in a manner which is unusual in the Santa Cruz Gravigrada, but very 

 common among the Pleistocene genera. 



