SCOTT : LITOPTERNA OF THE SANTA CRUZ BEDS. 1 5 



Milk Dentition. — The only example of the milk dentition which I have seen 

 in this genus is a young skull without mandible or premaxillary region ; all 

 the milk-premolars are in place, as is also m-, while m- is visible in the jaw, 

 but had not yet come into use. The temporary premolars closely resemble 

 their successors both in size and in pattern, but in all of them the two in- 

 ternal cusps are more distinctly separated, and dp- and -, at least, are 

 implanted by four roots, the internal pair of which differ from those of the 

 true molars in being of more nearly equal size, though the posterior root 

 is slightly larger than the anterior. 



^\\&Sktdl (Pis. II, figs. I, \a\ IV, fig. i) bears considerable resemblance 

 to that of the North American Oligocene genus, Merycoidodon [Oreodon), 

 though this resemblance is entirely superficial. The upper contour of the 

 skull is a nearly straight line from the occipital crest to th.e tips of the 

 nasals ; the cranium is long, with moderately full brain-case, which, however, 

 narrows much anteriorly ; the face is short and the whole skull is deep 

 dorso-ventrally in proportion to its length. The orbits, which are closed, 

 are large and have a somewhat oblique position, so as to present slightly 

 forward, as well as laterally. The sagittal crest is very prominent, especially 

 posteriorly, where the roof of the brain-case slopes downward. 



As a whole, the occiput is high and narrow ; on the ventral half, above 

 the foramen magnum, is a broad median convexity, with a shallow lateral 

 fossa over each condyle ; the dorsal half, which is extremely narrow, is 

 concave. The occipital crest is very prominent in the dorsal region, dying 

 away ventrally upon the paroccipital processes. These processes are long, 

 very broad and laterally compressed, almost plate-like, tapering distally 

 to a blunt point. The basioccipital is long and stout, with low and thin 

 ventral keel ; it is broadest about the middle of its course, narrowing 

 slightly toward each end. The condyles, which are formed entirely by the 

 exoccipitals, are rather small, but project prominently backward, and the 

 foramen magnum is relatively small. The exoccipitals are wide and low, 

 meeting in the median line ; on each is a low, blunt process, the two 

 separated by a deep median notch. The supraoccipital, which forms 

 somewhat more than the dorsal moiety of the occiput, is high and narrow. 



The periotic is exposed as a narrow strip in the deep, narrow cleft 

 between the exoccipital and the squamosal ; it does not form a mastoid 

 process. The tympanic was not ankylosed with the periotic and was but 

 loosely attached to the skull. I have seen no example of this bone, which 

 is missing from all the skulls at my disposal. 



