SCOTT : LITOPTERNA OF THE SANTA CRUZ BEDS. IO9 



enamel-lined fossettes, which, in the process of attrition, long remain as 

 enamel lakes. In advanced stages of wear, this tooth appears to have 

 quite the crown-pattern of a molar, though in unworn teeth the difference 

 is sufficiently obvious. 



The molars are highly characteristic and form a rather short series ; m- 

 and - are of nearly the same size, the former being, in some cases, slightly 

 wider transversely and shorter antero-posteriorly, though in others, m- is 

 a little the larger in both dimensions, while, in all cases, m- is consider- 

 ably the smallest of the series. The molar-pattern consists of two outer 

 crescents, which are quite deeply concave externally and meet in a promi- 

 nent median external pillar, or mesostyle ; and, further, there are two 

 small, conical, inner cusps, which are separated internally by a deep fissure, 

 or narrow valley, but are confluent on their outer margins [i. e., toward 

 the external side of the crown). Intermediate conules are present ; the 

 anterior one, as in p-, is a ridge, rising to an acute point, which is demar- 

 cated from the antero-internal cusp (protocone) by a cleft [i. e., in quite 

 unworn teeth), while the posterior conule is a ridge, sloping uninterruptedly 

 outward and backward from the postero-internal cusp (hypocone). A 

 spur of enamel extends from the hypocone transversely to the outer wall 

 of the crown, dividing the longitudinal valley into two fossettes, and in 

 some individuals, another spur projects from the postero-external cusp 

 into the posterior fossette, but this is a very variable feature. A third 

 fossette is enclosed between the much elevated anterior cingulum and the 

 protocone and anterior conule, and, in certain cases, a fourth and much 

 smaller fossette is formed between the two internal cusps and the internal 

 cingulum. This cingulum is, however, subject to great variation, and may 

 differ in degree of development on the opposite sides of the same indi- 

 vidual. In most of the skulls the internal cingulum is entirely absent 

 between the two internal cusps (proto- and hypocones) and, when present, 

 it may be a separate pillar, or a ridge connecting the two cusps and com- 

 pletely enclosing a fossette, or it may be attached to one cusp and not to 

 the other, making an imperfect fossette, which opens inward by a narrow 

 fissure (see PI. XVII, figs. 3, 3«). Always this cingulum, when present, 

 appears to be confined to m- and - ; I have seen no instance of its develop- 

 ment in m-. Variable as it is, this character can hardly have the generic 

 significance which Ameghino attributes to it. 



The third upper molar is distinctly smaller than m- or -, the reduction 



