PANTODONTA. 
191 
posteriorly round the crown, forming an open V, the external part of the 
crown consists of two V’s, as in Palceotherium, Palceosyops, etc. These V’s 
are equal in size, and a small vertical ridge, which divides them, is evidently 
homologous with the little ridge just described as existing near the posterior 
outer angle of the second molar. This tooth was in functional use at the 
time of the death of the animal. Immediately behind it, the surface of the 
maxillary bone is penetrated by the crown of the first true molar of the 
functional series. This presents the characters above ascribed to it in the 
adult, leaving no doubt of the systematic position of the animal, and the 
true relations of the teeth. 
The homologies of the different parts of the teeth are much elucidated by 
this specimen. It proves that the posterior principal, and anterior supple¬ 
mental V’s of the external portion of the crown of the superior permanent 
molars really represent the two external V’s of the ordinary Perissodactyle 
dentition, and that the external V of the first and second temporary molars 
represent the anterior V of the two found in the third temporary molar. 
A consideration of the permanent molars shows that the posterior crest of 
the last true molar is homologous with the two external V’s of the first and 
second; the external cusp of the former, which is sometimes separated by 
a cleft from the remaining portion, representing the rudimental anterior V 
of the latter. On comparing the premolars with the molars, the resemblance 
between the large posterior V of the true molars to the single V of the 
premolars is very apparent, but it is questionable whether this resemblance 
is a true homology. It is true that a small angle may be sometimes noticed 
at the anterior base of the V, which might be said to represent the anterior 
V of the true molars ; but the homology indicated by the temporary pre¬ 
molars is unmistakable, and may apply to the permanent premolars as well. 
A comparison of these teeth with those of other Amblgpoda, and with 
those of Perissodactgla, throws light on questions of affinity, since they are 
structurally somewhat intermediate between the latter and Loxolophodon 
and its allies. Among American Perissodactgla, an approach is seen in the 
genus Palceosyops, the structure of which furnishes an explanation of the 
relations between the structure of the superior molars of this and the 
Palseotheriodont types. From this comparison it appears that in Coryphodon 
