1887.] *^"-^ [Cope. 



unknown member of the Antliracotheroidea, which had bunodont teeth, 

 may form one of the missing links. Cebochoerus offers the proper type 

 of dentition, and the number of toes (four, Schlosser) is also appropriate, 

 but whether there are any structural obstacles to its being ancestral to the 

 Anoplotheriidse I do not know. 



Anthracotheriid?e can be properly supposed to have descended from a 

 type of Pantolestidge with well-developed lateral toes, by the addition of 

 the fourth tubercle, and the loss of the posterior intermediate ; while the 

 Dichobunidte have had the same origin, the posterior intermediate cusp 

 being preserved. The Xiphodontidse may be supposed to have come oflE 

 from the Anthracotheriida3 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 addition of 

 the fourth (posterior internal) tubercle to the superior molars. Some 

 genus with better developed lateral (second and fifth) digits than Panto- 

 lestes must have been the ancestor. Such a form will be discovered. It 

 has been already anticipated by Schlosser.* 



It is evident that the Listriodontidae form a special short side branch, 

 with a type of molar teeth, especially in the lower series, resembling some 

 of the Perissodactyla. The nearest approach to it is seen in the genus 

 Platygonus of the Suidoe, which has more complex premolars. Here the 

 four cusps of the quadritubercular bunodont type are fused together into 

 transverse crests. The limbs of Listriodon are unknown. 



It is a circumstpnce confirmatory of the view that the Cameloidea and 

 Booidea are descendants of the Anthracotheroidea rather than of the Suo- 

 idea, 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 Merycopo- 

 tamoidea already referred to. They did not probably come from the Mery- 

 copotamoidea themselves, since the geological age of the latter is too late. 

 Of course, however, members of this group may be yet discovered in 

 earlier formations. 



The problems of the phylogeny of the remaining groups are less diffi- 

 cult, and have been largely solved by the investigations of Kowalevsky 

 and Schlosser. Tragulidae have been derived from OreodontidiB with 

 simpler premolar teeth than the typical forms, [e. g. Dorcatherium and 

 Lophiomeryx). In turn they have given origin to primitive Bovidaa 

 (Cosoryx) through Gelocus, which have then branched off" into specialized 

 Bovidse on the one hand, and Cervidoe on the other. The Poebrotheriidse 

 have originated from some family with diminished lateral digits, perhaps 

 the Dichobunidse, various intermediate genera being yet unknown. They 



* Jlorphologisches Jahrliucli, 188G, p. 77, 



