ORIGIN, RELATIONSHIPS, AND PHYLOGENY 



29 



Cyclopidius stocks. With these I have placed certain other genera, either in a phylogenetic series 

 or as related branches, as shown on the accompanying chart (Fig. 2). The first two phyla I derive 

 from Eporeodon. The ancestors of the latter two must be sought in the middle or lower Oligocene 



Fig. 7. — Evolution of the basioccipit.il region in merycoidodonts. A. Merycoidodon culbcrtsonii, Cat. No. 595. 

 B. Merycoidodon gracilis, Cat. No. 596. C. Eforeodon bullatus, Cat. No. 611. D. Eporeodon major, Cat. No. 1038. 

 All specimens in A.M.N.H. cf, condylar (hypoglossal) foramen; flm, foramen lacerum medium; /?/>, foramen lacerum 

 posterius; jm, foramen magnum; fr, foramen rotundum; oc, occipital condyle; ff, paroccipital (paramastoid) process; 

 sf, foramen lacerum anterius (sphenoidal fissure); sm, stylomastoid foramen. (After Osborn and Wortman, 1894.) 



and are, I believe, derivatives of some form, perhaps like Merycoidodon gracilis on the one hand 

 or Limnenetes on the other, possibly the former for Merychyus and the latter for Leptauchenia- 

 Cyclopidius. This is a matter in which we cannot be dogmatic, as no connecting series leading to 

 either phylum has so far been discovered in Oligocene strata. 



The writer's present suggestion is that there was a parallel development on the West Coast 

 proceeding along the lines of the more eastern genera. In the western area I should derive the 



