SCOTT : ENTELONYCHIA OF THE SANTA CRUZ BEDS. 
251 
The disposition of enamel upon the molar-crowns is very peculiar. In 
unworn teeth the enamel is not reflected over upon the inner side of the 
external wall, or upon the hinder side of the anterior crest, or the front 
face of the posterior crest. The valley is thus enclosed in walls of enamel- 
free dentine, except near the base of the crown, where it reappears. In 
the abraded tooth, however, the enamel is again displayed as completely 
lining the valley and the resulting pattern is the same as though the 
unabraded crown had been entirely covered with enamel. 
The development of the cingulum varies greatly, but the differences 
are fluctuating and are not correlated with other characters ; apparently 
they are individual, not sexual, and have not the taxonomic significance 
which has sometimes been attributed to them. In Flower’s type: “All 
the teeth have crowns . . . with a well-marked cingulum around their 
base” (p. 175), but his figures seem to show that only m- has it on the 
outer face and even in this tooth the external cingulum is much less 
prominent than in the premolars, while all of the molars have it strongly 
developed on the internal, anterior and posterior sides of the crown. 
Ameghino states that the molars “have a cingulum on the inner, but not 
on the outer side” (’89^, 551), a conclusion which agrees with my own 
observations, for in none of the individuals which I have had an oppor- 
tunity of examining is there an external cingulum on any of the upper 
molars and it is variable on the other faces. In both of the La Plata 
specimens it is prominent on all sides except the outer one, while in one 
individual of the Princeton collection (No. 16,016), which agrees quite 
closely in size with the type of H. cunninghami , the cingulum is present 
only on the anterior and posterior faces and there is no trace of it on the 
inner side. In another of the Princeton specimens (No. 16,014), a smaller 
species, probably referable to H. segovice, the internal cingulum is partially 
and faintly developed on m-, and entirely lacking on m- and -. On the 
other hand, Ameghino’s type of H. segovice has a prominent internal 
cingulum. While invariably present, so far as I have observed, on the 
anterior face of all of the molars and on the posterior face of m 1 - and -, it 
varies even here in degree of prominence and tuberculation. 
The facts just cited make it clear that the development of the cingulum 
of the upper molars is subject to great fluctuation in specimens which, on 
every other ground, are referable to the same species. That the varia- 
tion is individual and not sexual is made extremely probable by the type 
