THE GEOGRAPHICAL DISTRIBL'TIOX OF ANTS. 151 



other. The southeastern and southwestern centers exhibit some blend- 

 ing of forms through an eastward migration from Mexico across the 

 Gulf States and a counter westward migration of forms from the 

 southeastern center. 



The southeastern center is characterized by several species of Doli- 

 chodcnts of the subgenus Hypodinca, closely related to the Eurasian 

 H. 4-notata. This group is not represented in the southwest. The 

 species of Sysphincta and Proceratium have been retained as relicts. 

 The latter genus seems not to occur in Eurasia. Several peculiar 

 species of Aphcenogaster (treatcc, mariff and laincllidens) have evi- 

 dently had their origin in the southeastern center, to which we must 

 also assign Pogonomyrmex badius, a single genus, Epcccns, and a sub- 

 genus of Lcpthothora.v (Dichothora.r). 



In the arid southwestern center there are a number of relicts which 

 seem to have been actively producing new forms since they were rele- 

 gated to this area. Such are the genera Liomctopnm, Myrmecocystus, 

 Messor and the subgenus Ischnomyrmex and the sections of the genus 

 Camponotns which comprise the species allied to C. maculatus and 

 falla.r. These forms are closely related to Old World species of 

 Indian origin. 



The admixture of adventitious tropical forms both in the south- 

 eastern and southwestern centers is considerable. In the latter these 

 have nearlv all arrived by way of Mexico, in the former many are of 

 Antillean provenience, but a certain number seem to be Mexican. The 

 genus Eciton, c. g., is well represented in Texas and there are a few 

 species in the Southeastern States. As this genus is not represented in 

 the West Indies or even in Florida, the eastern forms must have immi- 

 grated from the southwest. The same is true of species like Odon- 

 tomachns darns which is said to occur as far east as Georgia. 

 O. licematodcs, Xcnoiiiynne.r stolli, Cryptocerus various, Pscndo- 

 poncra stigma and Camponotns abdominalis, however, must have 

 entered Florida directly from the West Indies. It is equally clear that 

 Cryptocerus angitstus, the species of the Ponerine genera Pachycon- 

 dyla, Platythyrea, Xcoponera, Acanthosticlius and Ccrapachys, the Myr- 

 micine forms Macromischa and Xiphomyrmex and the Attiine genera 

 and subgenera Atta, Mocllcrius, Mycetosoritis, Trachymynnc.v and Cy- 

 pliomyrme.r (in part) reached the southwestern center from tropical 

 Mexico. Other genera widely distributed in the American tropics, 

 like Iridomvniic.r. Dorywynuc.r, Pscndoniynna, Stniinigcuys, certain 

 species of Poncra (crgatandria, trigona, opaciccps} and Camponotus 

 (maculatus and planatus') may have reached the adjacent portions of 

 the United States both from Mexico and the West Indies. This is 



