The Artiodactyla. 1083 
form one of the missing links. Cebochcerus offers the proper type 
of dentition, and the number of toes (four, Schlosser) is also appro- 
priate, but whether there are any structural obstacles to its being 
ancestral to the Anoplotheriidz I do not know. 
Anthracotheriidz can be properly supposed to have descended 
from a type of Pantolestide with well-developed lateral toes, by 
the addition of the fourth tubercle, and the loss of the posterior in- 
termediate ; while the Dichobunide have had the same origin, the 
posterior intermediate cusp being preserved. The Xiphodontide 
may be supposed to have come off from the Anthracotheriide by 
the usual process of diminishing the lateral digits and developing 
both sets of crescents in both superior and inferior molars. This 
family carried the specialization of the five tubercled type farther 
than any other. 
The Suoidea have come off from the Pantolestoidea by the addi- 
tion of the fourth (posterior internal) tubercle to the superior 
molars. Some genus with better developed lateral (second and 
fifth) digits than Pantolestes must have been the ancestor. Such a 
form will be discovered. It has been already anticipated by 
Schlosser,} 
It is a circumstance confirmatory of the view that the Cameloi- 
dea and Bodidea are descendants of the Anthracotheroidea rather 
than of the Suoidea, that no genus of the latter superfamily shows 
the least tendency to assume a selenodont structure of the molars. 
It is therefore not unlikely that the two groups named may have . 
had the history of the Merycopotamoidea already referred to. They 
did not probably come from the Merycopotamoidea themselves, 
since the geological age of the latter is too late. Of course, how- 
ever, members of this group may be yet discovered in earlier 
formations. 
_ The problems of the phylogeny of the remaining groups are less 
difficult, and have been largely solved by the investigations of 
Kowaleysky and Schlosser. Tragulide have been derived from 
Oreodontidæ with simpler premolar teeth than the typical forms, 
(¢.9., Dorcatherium and Lophiomeryx). In turn they have given 
origin to primitive Bovide (Cosoryx) through Gelocus, which have 
then branched off into specialized Bovide on the one hand, and 
1 Morphologisches Jahrbuch, 1886, p. 77. 
