scott: ENTELONYCHIA OF THE SANTA CRUZ BEDS. 257 
the tooth, except on the anterior and posterior faces, where it rises high 
upon the crown and dies away in the median line. 
The third premolar is closely appressed to po, so that it has a concave 
anterior face, where the enamel becomes very thin, or fails altogether ; 
and the cingulum is wanting, as it also is on the posterior face, at least in 
some individuals. The posterior crescent is both actually and relatively 
larger than in p^, equalling or slightly exceeding the anterior one in fore- 
and-aft diameter. The anterior valley is extremely shallow, so shallow 
that it can hardly be said to be present at all in moderately worn teeth, 
while the posterior valley is well-defined, considerably larger than in p^ 
and more widely open internally. The internal pillar (deuteroconid) forms 
a backward curving ridge, with convex inner face and, in conjunction with 
the posterior crescent, makes up a C-shaped masticating surface, which is 
more regular in outline than that of p ¥ . 
In p T the hinder crescent is still larger and more distinct than in pg and 
its posterior horn curves forward more sharply, while the valley of the 
anterior crescent is still extremely shallow. The internal pillar is a more 
elongate ridge and more nearly closes the posterior valley, so that the 
masticating surface formed by the ridge and the posterior crescent is of an 
almost complete, but very irregular oval shape. The cingulum is heavy 
and prominent on the internal and external faces of the crown, but incom- 
plete on the forward and hinder ends. 
All of the lower molars are very nearly alike, there being no such dif- 
ferences among them as are found in the upper series. In size, there is 
a moderate increase from m T to m ¥ , though m^ has the greatest transverse 
breadth. There is no talon or heel on m-3, as is generally the case through- 
out the order. Each of the molars is carried upon two broad roots, which, 
according to Ameghino (’89*, 552), are bifurcated near the free ends, but 
I have seen no specimens which make this point clear and therefore can 
make no comment upon Ameghino’s statement. 
All of the molars have the bicrescentic pattern common to all known 
Santa Cruz ungulates, but the anterior crescent is very short and the 
posterior one very elongate, the latter having more than twice the fore- 
and-aft length of the former. The external groove which demarcates 
the crescents is less deep and distinct than in the hinder premolars ; 
especially is this true of mi. While the forward crescent is far shorter 
antero-posteriorly than the hinder one, it is more complete, its posterior 
