EDENTATA OF THE SANTA CRUZ BEDS. 219 



No. 15,597- 

 ? , length ........................................ 008 .009 .007 



" width ......................................... 0073 .008 .007 



The skull (Plates XXXVIII, figs. 1-3, 5 ; XXXIX, figs. 1-3, 5, XL, 

 figs, i, i a ) is very variable in the details of structure and proportion, so 

 much so that no two specimens agree in these particulars, but on the 

 other hand, they all have a general similarity of size and appearance. It 

 is especially unfortunate that so few of the skulls are accompanied by the 

 mandible, because the absence of that bone often leaves the specific ref- 

 erence a matter of uncertainty. In all of the specimens the skull is long 

 and narrow, but considerable individual difference is observable in the 

 relative width, especially of the muzzle. Usually the occiput is quite 

 high and narrow, but varies considerably in proportionate height, and is 

 either vertical or slightly inclined forward. From the occipital crest the 

 upper contour of the skull rises with a degree of steepness which varies 

 with the height of the crest, that of the parietal eminence remaining quite 

 constant, and hence the rear view of the skull is very different in different 

 individuals. Anteriorly from the eminence, the upper contour is remark- 

 ably straight, forming a long, gradual and regular descent to the end of 

 the muzzle. The sagittal crest varies, probably with age, but is never 

 conspicuous ; it is absent, or, at most, very faintly indicated in the parie- 

 tal region, but is always present on the hinder half of the frontals in the 

 region of the postorbital constriction ; this constriction varies much in 

 depth and distinctness, but, as a rule, the whole anterior half of the skull 

 is much more slender than the posterior half. The rostrum is short and 

 narrow, with quite well-defined preorbital fossae. 



In none of the specimens are the sutures between the various occipital 

 elements visible, and evidently they are early obliterated. The supraoc- 

 cipital is produced for a short distance upon the dorsal side of the cranium, 

 but less extensively than in most species of the genus ; the occipital crest 

 is moderately prominent on the sides, becoming almost obsolete dorsally, 

 where it curves forward to accompany the supraoccipital. As a whole,' 

 the occiput is more or less convex, with median prominence for the ver- 

 mis, but without well-defined lateral fossae ; the dorsal margin of the fora- 

 men magnum is extended so as to form a short tube. The condyles are 

 small and sessile and usually approach each other quite closely on the 

 ventral side, where the foramen magnum notches the relatively broad basi- 

 occipital. No distinct paroccipital processes are present. 



