252 
PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 
of H. cunninghami, which has an exceptional development of the cingulum 
and yet would appear to be a female, as indicated by the small size of 
the canines. 
Like the premolars, the molars are each carried upon three very long 
roots, of which the two external ones are comparatively slender and the 
internal one is very large, extending for the whole antero-posterior length 
of the crown. This inner root, however, is obviously formed by the 
coalescence of two roots and on the buccal side the fusion is incomplete, 
a ridge of bone in the alveolus partially separating them. 
The first molar (m- 1 ) is considerably larger than p- and has a sub- 
quadrate crown, the antero-posterior and transverse diameters of which 
are nearly equal. The external face is nearly smooth and convex, but 
there is a low vertical ridge near the anterior border, which is much less 
conspicuous than in the premolars. This ridge is followed by an extremely 
shallow concavity and, opposite the posterior transverse crest (meta- 
loph), by a second very faintly marked ridge. The outer face is thus 
feebly sinuous. From the external wall two transverse crests are directed 
inward, ending in the two internal cusps, the proto- and hypocones, with 
which the crests are indistinguishably fused. Even in quite well worn 
teeth these transverse crests are widely separated internally by a broad 
and deep valley, which is the most obvious difference from the premolar 
pattern. The crests are nearly transverse in direction and are less oblique 
than in the rhinoceros molar, but, owing to the shape of the valley, the 
posterior crest is much shorter than the anterior. The external wall of 
the crown extends well behind the metaloph, with which it partially 
encloses a shallow fossa. As the valley is much deeper toward the 
external side, its internal opening is obliterated with the progress of 
abrasion and the valley is converted into a narrow, elongate lake, which 
has an oblique course, running backward and inward. At this stage of 
wear the difference in pattern between molars and premolars is far less 
obvious than in the unworn condition. 
The second molar differs from m 1 chiefly in its greater size, especially 
in the antero-posterior diameter, and in a slightly greater complexity of 
pattern. In the fresh and unworn state the two internal cusps are very 
widely separated by a broad, V-shaped notch, the inner opening of the 
valley. The anterior crest is simple and nearly straight and a shallow 
notch demarcates it from the external wall of the crown, but this notch 
