SCOTT: ENTELONYCHIA OF THE SANTA CRUZ BEDS. 
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oblique ridge and a much larger one by the fourth spur, the ridge, the 
metaloph and the outer wall, but the latter fossa opens posteriorly between 
the metaloph and the wall. The inner face of the wall is very rough and 
given a wrinkled appearance by numerous irregular vertical ridges of 
dentine. 
The third upper molar, in the unworn condition, thus differs from m 1 
and m- in several particulars, which maybe thus summarized: (1) the 
triangular shape of the crown; (2) the presence of a large, conical, acces- 
sory tubercle on the posterior side of the protocone ; (3) the great reduc- 
tion of the posterior transverse crest and its wide separation from the 
external wall ; (4) the presence of four separate spurs projecting inward 
from the outer wall. 
The appearance of the tooth is much changed by abrasion, though the 
characteristic triangular shape of the crown is always retained. The 
accessory tubercle, the oblique ridge and the spurs are all worn away 
and the metaloph becomes connected with the external wall, but remains 
conspicuously short ; the valley is converted into a narrow, oblique slit 
and, in old animals, into a closed lake, while the enamel lining of the 
valley is displayed. In this abraded condition the resemblance to the 
other molars is much closer. 
B. Lower Jaw (PI. XXIX, figs. 1, 1 a ). — Mandibles are even more 
rare in the collections than skulls and such as are known belong in nearly 
all cases to old animals. I am therefore unable to give as complete an 
account of the inferior dentition as of the superior, having seen no 
examples of quite fresh and unworn teeth. The youngest specimen 
known to me is Flower’s type of H. cunninghami. 
The incisors are smaller than those of the upper series, but quite similar 
to them in form ; they are comparatively simple, compressed-conical 
teeth, with acute points, trenchant edges and prominent cingulum, and 
grow larger from iy to iy. The third incisor is figured by Flower {t. c., 
PI. XVI, figs. 2, 3) in an almost perfect state and shows on the internal 
face “a vertical ridge running from base to apex of the crown, rather 
nearer the anterior than the posterior edge of the tooth” (pp. 177-8). 
The canine in the type of H. cunninghami , and in a mandible of the 
Ameghino collection referred to the same species, is larger than iy, but 
considerably smaller than the upper canine. Whether in the supposed 
males with enlarged upper canine, the lower tooth is also tusk-like, can- 
