KEY TO THE XOKTII AMERICAN FORMICIDJE. 559 



8. Large >pecie> ; workers highly polymorphic; head with only one pair of 



occipital spines; thorax with three pairs of dorsal spines or tubercles. 



Atta Fabr. s. str. 



Smaller species; workers monomorphic or feebly polymorphic; thoracic 

 dorsuni with four pairs of spines or tubercles >>. 



9. Head broad, with rounded occipital lobes, without supraocular spines or 



tubercles Subgen. Ma'llcriits Emery. 



Head narrow, with angular occipital lobes; body rough, covered with small 



tubercles Subgen. Trucliyiiiyniie.i- Forel. 



10. Antennae with a 2-jointed club i 1. 



Antennal club, when developed, with more than two joints 12. 



i i. Antennae lo-jointed ; epinotum unarmed Solcnopsis Westw. 



Antennae ii-jointed ; epinotum dentate Ercbomyniui Wheeler. 



12. Posterior margin of clypeus elevated in the form of a welt or ridge bordering 



the antennal fossa in front 13- 



Posterior border of clypeus not thus elevated 15- 



13. Portion of clypeus in front of the antennal insertion narrow but not. reduced 



to a mere ridge (antennae of male lo-jointed ) M- 



Portion of the clypeus in front of antennal insertion reduced to a mere ridge 

 (antennae of male ij-jointed) Mynnccina Curtis. 



14. Antennas i2-jointed Tctramorium Mayr. s. str. 



Antennas ii-jointed Xipliuinyniic.r Forel. 



15. Antennas n -jointed lO. 



Antennas i2-jointed 19. 



16. Thorax and petiole without any traces of teeth or spines; pronotum never 



angular 17. 



Epinotum armed with spines or teeth 18. 



17. Petiole distinctly pedunculate Monomorium Mayr. 



Petiole not pedunculate Xcnom\nnc.\- Forel. 



iX. Mesoepinotal constriction distinct; males ergatomorphic. 



Symmyrmica Wheeler. 

 Mesoepinotal constriction faint or lacking Lcptotliora.v Mayr. 



19. Workers strongly dimorphic, usually without intermediates connecting the 



extreme forms; antennal club j-jointed, longer than the remainder of the 



f uniculus Phcidolc Westwood. 



Workers monomorphic or polymorphic, /. c., with mediae intermediate between 

 the major and minor forms; antennal club indistinct or shorter than the 

 remainder of the funiculus 20. 



20. Last three antennal joints much shorter than the remainder of the funiculus 



and not forming a distinct club 21. 



Last three antennal joints forming a distinct club 'nearly as long as the re- 

 mainder of the funiculus 26. 



21. Thoracic dorsum impressed at the mesoepinotal suture; promesonotal suture 



usually distinct 22. 



Thoracic dorsum without any traces of suture or impression 



Pogonomyrmex Mayr. 



22. Posterior tibial spurs pectinated Myrmica Latr. 



Posterior tibial spurs simple 23. 



23. Small hypogasic species, with vestigial eyes and two keels on the clypeus. 



Steuaiiiina Westwood. 



Medium sized species, with \vell-developed eyes and no keels on the cly- 

 peus 24. 



24. Workers monomorphic 25. 



Workers polymorphic Mcssor Forel. 



25. Cosmopolitan species with moderately slender thorax and legs. 



Aph&nogastcr Mayr. s. str. 



