256 
PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
not be determined from the available material. In Flower’s specimen 
the lower canine is very similar to h in form, but is less regularly conical, 
the crown is more elongate antero-posteriorly and thicker transversely, 
and the vertical ridge on the inner side is more prominent and massive. 
The premolars are all different from one another and from the molars, 
though pi approximates the latter in structure and p3 does so also, but 
in a less marked degree, the transition from py to py being very gradual. 
The first premolar is subject to considerable variation in size, which may 
be specific, or only individual, and to some fluctuation in form. In the 
type of H. cunninghami py on the left side has a smooth, convex and 
undivided external surface, while on the right side there is an incipient 
division into two lobes visible on the outer face. (Flower, t. c., p. 178, 
PI. XVI, fig. 2.) This division into two crescents becomes more con- 
spicuous and the posterior one grows larger on each successive tooth of 
the premolar series. In a specimen of the Princeton collection (No. 
16,015) which agrees almost exactly with the type in size, py on both 
sides of the jaw has a simple and rounded outer surface without trace of 
a division. Internally, the valley is divided into anterior and posterior 
portions by a vertical, wedge-shaped ridge, the deuteroconid, which is 
broad at the base and narrows regularly to the apex. In the unworn 
tooth, of which I have seen no examples, this apex no doubt forms a dis- 
tinct and separate cusp, but after a very brief period of wear it becomes 
confluent with the external wall. The broad and shallow posterior valley 
has a tubercle and one or two short, vertical ridges of enamel, which 
differ in number and prominence on the two sides of the jaw. The 
cingulum is very prominent all around the crown. 
The first premolar is implanted by a single root, the others have each 
two roots, which Ameghino states (’89*, 552) are again divided, each into 
two, near the tip. I am unable to confirm or dispute this statement. 
The second premolar is plainly divided by a deep external groove into 
two imperfect crescents, of which the anterior one is the larger ; its internal 
valley is shallow, but distinctly marked, while that of the posterior crescent 
is small but deep, and has an extremely narrow internal opening, owing 
to the backward extension of the internal pillar (deuteroconid) which arises 
at the junction of the two crescents, and also to the forward curvature of 
the hinder horn of the posterior crescent. The valley is thus soon con- 
verted into a lake by abrasion. The cingulum is prominent all around 
