420 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 
antemolars, instead of explaining their exceptional number as due to 
reduplication. This is the same dental formula as in the Didelphyidm. 
It is occasionally observable in Ccenolestes , as noted by Bensley (1903, p. 
124, PL 5, fig. 38). 
The proximal half of the median incisor is preserved. As in Ccenolestes , 
the enamel layer is confined to the outer side of the crown. So far as 
can be judged from the part preserved, this tooth was of much the same 
shape as in Ccenolestes . Following the enlarged incisor are five minute 
teeth closely crowded and more or less pronate, which are interpreted as 
three incisors, a canine and the anterior premolar. The anterior two are 
represented by alveoli. The first alveolus is displaced toward the inner 
side, lying beside instead of in front of the third incisor. The lateral in- 
cisor, the canine and the anterior premolar are identical in shape. The 
median and posterior premolars are double-rooted functional teeth. Both 
carry large heels, that on the median premolar being much larger than 
Fig. 7. 
Halmavhipkus nanus , right ramus, crown view, x f (No. 9593 American Museum of Natural 
History). 
that on the posterior tooth. The crowns are laterally compressed, with the 
principal cusp high and recurved. An anterior accessory basal cuspule 
of microscopic proportions is observable on the inner side of the crown. 
The first molar is not differentiated as a sectorial and is slightly smaller 
than the second. The third is narrower than the second, and the fourth 
quite small. All display the tuberculo-sectorial pattern (text fig. 7). The 
trigonid is narrow, with the cusps separated by sharp notches. The talonid 
is broad, with the hypoconid and entoconid enlarged and the hypoconulid 
small, but distinct. The cusps of the trigonid and talonid are elevated to 
the same general level in the three anterior molars. In the fourth, the 
heel is depressed. The protoconid is slightly higher than the metaconid 
in the first molar, but of approximately the same elevation in the second, 
third and fourth. A prominent external cingulum is present on all the 
molars, as in Ccenolestes and Didelphys. 
