RHYNCHIPPUS oI 
between them an elongated basin, which, as in the pre- 
molars, becomes, on wear, a pit extending obliquely across 
the tooth. 
The lower incisors have no furrows in the crowns, but 
in this genus there is a small cingulum on the inner side 
just above the base of the enamel. The lower canine is 
incisiform, and also has the basal cingulum. Each of the 
premolars has, on the external side, a median vertical 
groove, beginning at the base of the enamel, and widening 
toward the top. This is progressive if less marked from 
pm. 1 to pm. 4. The premolars and molars consist essen- 
tially of two crescents, the shorter anterior, and the pos- 
terior which is about twice as long as the anterior. The 
details are as described on page 96, and seen in figure 55. 
The skull is of moderate height, nearly flat on top with 
wide zygomatic arches. The sagittal crest is moderately 
high, and slightly convex in the antero-posterior direction. 
The occipital region is overhanging and topped by short 
lambdoidal crests, which, extending to either side, unite 
with the zygomatic arches. The nasals are large, roughly 
rectangular, and slightly constricted just in front of the 
middle. The frontals are short, and project over the orbits 
in strong processes. The maxilla is large, bounding the 
front of the orbit, and extending backward in a strong 
zygomatic process which makes nearly half of the arch. 
The jugal, while stout, is short, and reaches from the long 
zygomatic process of the maxilla to the short one of the 
squamosum. The lachrymal bone is tiny, with a low tu- 
bercle, just below which is situated the lachrymal duct, 
just on the margin of the orbit. Just behind the zygomatic 
arch, the squamosum is inflated and contains a large hol- 
low chamber, as is typical among toxodonts. The mastoid 
bullae, while relatively small, are swollen into a globular 
form, and have a large hollow chamber. ‘The palate ex- 
tends back to just behind the last molar, a feature distin- 
guishing this genus from Morphippus. 
