15 ANTS. 



times. Although these have spread from their centers of origin and 

 intermingled with the northern circumpolar fauna, they have not IKVH 

 sufficiently displaced to prevent the recognition of the four centers of 

 dispersal which Adams calls the northeastern, northwestern, south- 

 eastern and southwestern respectively. (_)f these the first has con- 

 tributed very little, the last more considerably to our ant-fauna, and 

 tin- northeastern and northwestern have more species in common than 

 the other two centers. The former, in addition to the subboreal types 

 above mentioned, is characterized by the following : Stigmatomma 

 pallipcs, Crcmastogaster lineolata, Camponotus falla.v, Prcnolepis 

 imparts, I'o/ycr^ns and the species of Lasius of the subgenus Acan- 

 tlnnnyops. These species, however, are often represented by distinct 

 eastern and western subspecies and varieties and usually the western 

 are more closely related to the Eurasian than to the eastern forms of 

 the species. This difference in relationships is even more striking when 

 distinct but allied species are compared in the two centers. Thus the 

 western Stenamma nearcticum is more closely related to the European 

 5\ westwoodi than to the eastern S. brevicorne ; the eastern Aphccno- 

 gastcr fuk'a is represented in the west by A. occidcntale which is 

 merely a variety or subspecies of the European A. subterranea; the 

 eastern Camponotus falla.r. Formica rnfa and Pol\crgns hicidns 

 are represented in the western region by subspecies or varieties very 

 much like the Eurasian forms. The northeastern center retains at 

 least three relicts, Mynnecina graminicola, Poncra coarctata and 

 Harpagoxenus common to the Eurasian fauna, but apparently absent 

 from the northwestern center; whereas Mynnica iinitica, which is 

 hardly more than a subspecies of the European M. nibida, occurs 

 only in the mountain valleys of the northwest. This center also has 

 three genera, Symmyrmica, Sympheidole and Epipheidole, not known 

 to occur elsewhere. These are, however, parasitic species and have 

 probably developed from LeptJwthora.r- and Pheidole-like forms within 

 comparatively recent times. Although several species of Acantho- 

 myops occur in the Rocky Mountains, representatives of this sub- 

 genus are far more abundant in the northeastern center from which 

 they probably radiated. On the other hand, the species of Formica 

 allied to the European F. rufa have had their center of origin and dis- 

 persal in the northwest. 



The southeastern and southwestern centers contain more relicts of 

 the southern preglacial fauna and have, moreover, received many acces- 

 sions from the fourth, or tropical wave which started in South Amer- 

 ica, probably in Archiguiana, and reached North America by way of 

 Central America and Mexico on the one hand, and the Antilles on the 



