460 Bulletin American Musemn of Natural History. [Vol. XXVII, 



(6) The Cetacea are certainly typically Cseneutherian, both in respect 

 to their extraordinarily progressive brain and their post-Basal-Eocene radia- 

 tion. But the collateral ancestors of the Cetacea, namely the earliest Zeug- 

 lodonts, have a low type of brain (p. 417) and are probably derived from 

 some Meseutherian Insectivore-Creodont family. 



(7) The Anthropoidea are typical Cteneutheria but there can be little 

 doubt that they have been derived from Eocene Lemuroidea of some kind. 

 This is indicated not only by the fundamental resemblances between existing 

 members of the two suborders and the union of certain of their most dis- 

 tinctive characters (p. 321) in the genus Tarsius, but also by the existence of 

 Lower Eocene Primates (Notharctidje) which are classed by some authors 

 as Lemuroids, by others as early Anthropoids. The Lemuroidea were placed 

 by Osborn (/. c, p. 236) among the Meseutheria. Certain forms (e. g., 

 Indrisina^) have a richly convoluted cerebrum (Weber, 1904, p. 748); the 

 more primitive ones have a relatively low brain type: the olfactory parts 

 of the brain and the ethmoturbinal complex (p. 428) clearly indicate deriva- 

 tion from macrosmatic animals with a brain of the typical INIeseutherian type. 

 The Lemuroidea have very probably been derived from progressive Insecti- 

 vores with relatively large brain, analogous to Tupaia (p. 321). 



Hence, whether the Lenuiroidea be regarded as Meseutheria or Cieneu- 

 theria, it follows that the order Primates has been derived from a Meseuthe- 

 rian source but not necessarily from any wqW known Basal Eocene genera. 



(8) The Rodentia are not known until the Lower Eocene and are there- 

 fore classed by Osborn as Cseneutheria (/. c, 1909, p. 33) but even in the 

 existing families the brain in the more primitive forms is of very low type, 

 the hemispheres being small and smooth and not overlapping the cerebelhmi 

 (Weber, p. 478), while the rhinencephalon is large; in the characters of the 

 ethmo-turbinal complex, and in all the characters of the skeleton the llodentia 

 retain traces of derivation from some unknown Basal Eocene or Upper 

 Cretaceous, insectivorous Meseutheria. 



(9) The Insectivora (especially the Zalambdodonta) are tyi)ically 

 iNIeseutherian in brain structure and in whatever "incapacity for progressive 

 evolution" may be implied in the retention of a large number of extremely 

 primitive characters in the existing forms. But as noted by Osborn, the 

 Leptictidpe, which are approximately ancestral to the Erinaceida', appear to 

 have come in with the Lower Eocene " Cieneutheria," while certain Insecti- 

 vores {Tupaia) have a relatively large brain case. The Insectivore-Creodont 

 group also a])pears in fact to be largely prototypal (p. 253) to both the 

 INIeseutherian and Ciencutherian orders. 



(10) The Edentates are left "Incertse Sedis'' in the original description 

 of the Meseutheria and Eutheria. The Edentata-Tseniodonta (Gano- 



