Charles Earle—-Evolution of the American Tapir. O95 
consist of only a single internal cone. This species is nearly as 
large as its successor in the upper layer of the Lower Miocene. 
The best known American species of Protapirus is the P. obliqui- 
dens from the Protoceras beds of the Lower Miocene. This species 
is represented in the American Museum Collection by the upper 
and lower dentition, and a finely-preserved manus. The comparison 
of the upper premolars of P. simplex with those of P. obliquidens 
reveals the fact that the internal cones of these teeth in the latter 
_ Species are in a transition stage of development, and are intermediate 
in structure between those of the earliest species of Protapirus, viz. 
P. simplex and the recent Tapir. In the genus Tapirus the last 
three superior premolars are truly molariform, and consist of two 
external cones and two complete transverse crests; the latter being 
entirely separated internally. Now in P. obliquidens the internal 
cones of these teeth are deeply bilobed at their summits, especially 
the last two of the series; the anterior crest is well marked, but the 
posterior less so. It is interesting, from a phylogenetic point of 
view, to notice that the anterior crest of the premolars in the 
Tapiride is the first to be developed, and later the posterior appears 
by an elongation transversely of the posterior intermediate tubercle. 
The characters of the upper true molars of Protapirus obliquidens 
are nearly the same as those of Tapirus; their peculiarity is the 
obliquity of the external lobes and also of the posterior crest. 
The lower jaw of the American Lower Miocene Tapir is nearly as 
large as that of the Brazilian Tapir. The inferior premolars, like 
the upper, are simpler in structure than those of the recent Tapir ; 
this applies especially to the posterior crest, which is undeveloped. 
We find that the last lower true molar has lost the large third lobe 
so characteristic of the Eocene Tapirs of America. 
The foot structure of the American species of Protapirus shows 
that it is nearly identical with the recent form. In contrast with 
the Brazilian Tapir we notice the greater size of the fifth toe in 
comparison with the middle digit. The elements of the carpus are 
much displaced in Protapirus, and only differ from the recent Tapir 
in their rather more elongated form. 
One of the contemporaries of Protapirus in the Lower Miocene of 
America is the genus Colodon (Mesotapirus, 8. & O.). This Tapiroid 
resembles Protapirus somewhat in the structure of its teeth, but in 
the lower jaw the external incisor is absent. We can readily dis- 
tingnish between the true l'apirs and the pseudo-Tapirs of the Lower 
Miocene by the form of the postero-external lobe of the superior 
molars, as already described. The structure of the manus of Colodon 
differs considerably from that of Protapirus. In the former genus 
the fifth digit is very small, and there is some enlargement of the 
middle digit. In fact the structure of the manus in this genus 
proves that it was tending towards monodactylism; this is also 
shown from the reduced size of the ulna as compared with the size 
of the radius. Phylogenetically Colodon is now considered to be 
the outcome in the Miocene of the Bridger (Eocene) genus Helaletes. 
In Tapiravus, Marsh, from the Pliocene the last two premolars 
