24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 69 



great gap exists in our knowledge of the contemporaneous fauna of 

 Central America, and northern South America may have been iso- 

 lated by an Amazonian gulf. Various authorities, however, includ- 

 ing Hill," and Scott "^ concur in the belief that North and South 

 America have been united from the Miocene to the present time. 

 Intermigratory movements, probably setting in during the Miocene 

 period, extended through the Pliocene and into the Pleistocene when 

 the interchange of mammalian groups reached its maximum and was 

 followed by extensive extinction, leaving both regions comparatively 

 impoverished. Notably numerous contributions from the North 

 American fauna have, however, persisted and maintain a high state 

 of development in Central and South America. 



The mammalian fauna of Panama, as a whole, is South American 

 in the sense that most of the genera and many of the species are 

 common to both regions. 



The eastern and western parts of the republic with the Canal Zone 

 as a convenient dividing line, however, present important faunal 

 differences. The former section is more truly South American, 

 especially the mountainous parts, while western Panama partakes of 

 the character of the Central American subregion. The following 

 genera range from South America into eastern Panama, but are not 

 known from the western part of the republic : Peramys, Rhipi- 

 domys, Neacomys, Diplomys, Hydrochcerus, Icticyon, Lonchorina, 

 Macro phylluw., Lonchophylla, Vampyressa, Molossops and Leonto- 

 cebus. Some of the bats may not improbably prove to be more widely 

 distributed in Central America, but the limits of the other genera 

 in that direction are believed to be approximately fixed. Several 

 rodent genera assignable to the Central American subregion are 

 apparently restricted in the republic to the highlands of the western 

 part, as follows : Nyctoinys, Scotmomys and Synth eosciiirus. A 

 few North or Middle American elements, as Reithrodontomys, Pero- 

 myscus, Macrogeomys and Cryptotis, reach the mountains of extreme 

 eastern Panama or cross the Colombian frontier, but are not known 

 from the Canal Zone. 



The tendency of the Canal Zone to delimit faunas is indicated by 

 the distribution of various species. The genus Saimiri ranges in 

 South America and is apparently absent in eastern and central 



* Hill, R. T. The Geological History of the Isthmus of Panama and Costa 

 Rica. Bull. Mus. Comp. Zool., Vol. 28, p. 270, June, 189S. 



' Scott, W. B. The Isthmus of Panama in its Relation to the Animal Life 

 of North and South America. Science, N. S., Vol. 43, No. iioo, p. 117, January 

 28, 1916. 



