548 mscussioN on results recorded 



American deposits to support the tlieory of its former extension 

 into northern latitudes. 



RoDENTiA.— The headquarters of the Hystricomorpha at the 

 present time are South America, where they date back to the 

 Upper Miocene. The only North -American representative of 

 the gi'oup is the tree-porcupine {Erethizon), a late immigrant 

 fi-om South America. No extinct representatives of the group 

 have been found in early or mid-Tertiaiy strata in North 

 America. But in the Old World alleged representatives of 

 the suborder, referred to the family Theridomyidse, occur in 

 Eocene and Oligocene deposits in Europe, and at the present 

 time several genera of Octodontidse occur in Africa, and the 

 Hystricidse range from Africa through Southei^n Asia to Boi'neo. 



Until evidence for the existence of this group in early and 

 mid-Tertiary or Cretaceous times in North America is forth- 

 coming, it cannot reasonably be claimed that the South-American 

 forms are descendants from ancestors from the Noi'th ; and if the 

 theory of raft-transportation from Africa be rejected, it must be 

 conceded that the faunistic similarit}^ between troj^ical America 

 and Africa in this respect supports the idea of a transatlantic 

 land-connection between those countries. 



Primates. — The past and present distribution of Monkeys 

 is tolerably similar to that of the Hystricomorph Rodents. The 

 Platyrhini are restricted to South and Central America, Avhere 

 they date back to the Upper Miocene. No fossil monkeys 

 have hitherto been discovered in North America. Similarly, the 

 Catarhini are confined to ti'opical and temperate countiies of 

 the Old World, and have been recorded from middle and later 

 Tertiary deposits in Europe and Asia. The available data, there- 

 fore, point to the entiy of monkeys into South America from the 

 Old World by means of a southern transatlantic land-bridge, 

 unless it be claimed, as it has been claimed, that the resemblances 

 between the Platyrhini and Catai-hini ai-e due to couA^ergent 

 descent from Lemuroids of the New and Old Worlds respectively, 

 a vieAv from which Mr. Pocock expressed dissent. 



Dr. C. W. Andrews, F.E.S., F.Z.S., remarked that if a land- 

 bridge had existed between Africa and South America in Tertiary 

 times one would expect a more extensive mingling of faunas than 

 had actually taken place. Even in the Eocene both continents 

 must have had a varied mammalian fauna, yet it is only claimed 

 that the Primates, the Hystricomorph Rodents, and perhaps 

 some Insectivora crossed from Africa to South America, no inter- 

 change in the opposite direction being known. Of these groups 

 the Primates are represented by numerous small lemur-like 

 animals in the Eocene of North America, and it is thence that 

 the colonization of South America probably took place, although 

 at present the gi-oup may be unknown from the older tertiaries 

 of that continent. The Hystricomoiph Rodents are represented 

 \n the Eocene and Oligpcpne of the Old Wo^kl by nmnerous. 



