146 PATAGONIAN EXPEDITIONS I PAL/EONTOLOGY. 



those of the other species, especially in the conspicuous subdivision of the 

 postero-external lobe, the chief difference being in the somewhat smaller 

 size and proportionate narrowness of these teeth in the present species. 

 Another important difference is in the great vertical height of the teeth in 

 C. debt/is. 



MEASUREMENTS. 



Upper dentition, length ? .092 , length 013 



J-, length (*.<., antero-posterior diameter)?. 006 " width 006 



2, length 0075 , length 0125 



" width (*. e., transverse diameter) 0045 " width 007 



A, length .010 1, length 012 



" width 0045 " width 007 



A, length 012 A, length 0115 



" width 005 5 " width 007 



The skull (Plate XXVIII, figs. 3, 4), while very like that of C. muri- 

 catus in its general appearance and proportions, yet differs from it in a 

 number of not unimportant particulars. The occiput is notably higher and 

 narrower, in which respect it differs decidedly from that of any other 

 known Santa Cruz glyptodont ; the occipital surface is quite deeply con- 

 cave and has no median prominence for the vermis of the cerebellum. 

 This concavity is largely due to the development of the occipital crest, 

 which is not only prominent, but unusually thick and massive, especially 

 on the sides. The occiput also has a slight forward inclination, which, 

 however, is not so distinct as in Metopotoxus, and in side-view is some- 

 what concealed by the prominent crest. When the plane of the teeth is 

 held horizontally, the basicranial axis has a slight inclination downward 

 and forward. The periotic is quite largely exposed upon the surface of 

 the cranium and ends ventrally in a very blunt and heavy mastoid process. 



The zygomatic arch has, in an exaggerated degree, the peculiarities 

 seen in C. muricatus ; the posterior portion is horizontal, while the ante- 

 rior descends more steeply, making the angulation of the ventral border 

 more distinct and giving a more oblique position to the orbit ; the glenoid 

 cavity is raised higher above the level of the teeth than in any other 

 known Santa Cruz glyptodont. The preorbital fossa in the maxillary is 

 much better defined than in C. muricatus, but is hardly visible when the 

 skull is viewed from above. The alveolar portion of the maxillary has a 

 greater vertical extension than in any other contemporary glyptodont, and 

 to this is due the greater elevation of the glenoid cavity and the steeper 



