EDENTATA OF THE SANTA CRUZ BEDS. 297 



MEASUREMENTS. 



No. 15,361. No. 15,901. Amegh. Coll. 



Lower dentition, length 031 .033 .032 



j_ T 024 .024 .024 



r , length 006 .0065 .008 



" width 005 .0045 .006 



-%, length 007 .006 .006 



" width 009 .009 .010 



3, length 008 .0065 .006 



" width OIO .010 .010 



-f, length 009 -0075 .008 



" width 009 .009 .008 



N. B. Some of the discrepancies in this table are due to the fact that in No. 15,361, and No. 

 15,344, except in the case of , the dimensions are taken from the empty alveoli. 



The skull (Plates L ; LI, fig. 4), though varying considerably in differ- 

 ent individuals, is one of the most characteristic in the entire series of 

 Santa Cruz Gravigrada ; its appearance is much changed in those indi- 

 viduals which have undergone even a slight amount of vertical compres- 

 sion, which diminishes the remarkable elevation and vaulting of the cra- 

 nium (compare figs, i and 2, PI. L). This skull is peculiar in its low 

 occiput, high and dome-like cranium, short and deep postorbital constric- 

 tion, broad forehead and short, wide rostrum. The upper contour is 

 quite sinuous ; it rises more or less steeply to the parietal eminence, which 

 is somewhat farther forward than the glenoid cavity ; from this point, the 

 line, sometimes concave, descends to the postorbital constriction, becom- 

 'ing convex over the forehead and descending gently to the end of the 

 rostrum. Seen from above, the aspect of this skull is equally character- 

 istic, the anteriorily inclined occipital crest curves forward in the middle 

 dorsal region, invading the roof of the cranium ; the short postorbital 

 constriction is deep and abrupt, the skull rapidly broadening again to the 

 forehead, which has temporal ridges that are much more prominent in 

 some individuals than in others ; the lachrymals are only moderately 

 prominent and the preorbital fossae are not visible from above ; the ros- 

 trum is short, narrowing slightly forward, blunt at the end and some- 

 what decurved, recalling the shape seen in many rodents. 



The occipital surface, which has a forward inclination, is broad and 

 unusually low ; the ventral portion is transversely convex and is produced 

 outward above the foramen magnum, giving the latter a tubular form, 



