1895.] Parallelism in the Genus Palaeosyops. 625 
series were parallel in many of their characters, although the 
P. megarhinus-Telmatotherium division did not commence to 
differentiate those characters which are found in Titanothe- 
rium as early as the P. laticeps-P. vallidens series. 
In the following table I have arranged some of the species 
of Palaeosyops phylogenetically and in three parallel columns, 
two of which are supposed to contain persistent types. The 
third column contains the more specialized species, which are 
are supposed to have died out. 
In conclusion I wish to emphasize the following points :— 
The first series exhibits transition in the structure of the 
the teeth and skull which is quite gradual, although in the 
most highly differentiated form of this line, namely, Telmato- 
therium sp. nov. (type specimen in American Museum collec- 
tion), the dorsal contour of the skull is slightly convex and 
not saddle-shaped as in Titanotherium. This series began to 
differentiate later, as already shown, than the second series ; 
this is proven by the presence in the Bridger proper of the 
supposed earliest members of the two lines, namely, P. mega- 
rhinus, which has a skull with a nearly straight dorsal contour, 
and the ancestor of the second line, namely, P. laticeps, with a 
skull which is deeply concave like that of the White River — 
genus Titanotherium. 
2. The changes from P. laticeps to P. vallidens parallels that 
of the first series in many ways, notably the increased height 
of the crowns of the molars, reduction of the intermediate 
tubercles, increase in size of the skull, and lastly some indica- 
tions of the development of horns. 
3. The great variety of species occurring in the genus 
Palaeosyops indicates progression and advancement towards a 
higher type, although we observe that a number of the species 
probably left no descendants. In the genus Titanotherium, 
which was approaching extinction, we see fewer well marked 
species and much closer similarity between them than between 
those of Palaeosyops. 
