SYSTEMATIC POSITION. 27 



The subfamily Dolichoderinse contains six North American genera : 

 Dolichodcriis (Hypoclinea), Forelius, Tapinoma, Dorymyrmex, Lio- 

 metopiim, and Iridomyrmex. Iridomyrmex is essentially tropical in 

 its distribution and only two species arc known to occur in the United 

 States/ the native Iridomyrmex analis Ern. Andre, common in cotton 

 fields of the South, and the introduced species, Iridomyrmex Jiumilis 

 Mayr, or Argentine ant. 



DESCRIPTION OF THE SPECIES. 



Three forms only of the adults are found in the colonies of the 

 Argentine ant, the females or queens, the workers, and the males. 

 (See fig. 6.) Major and minor workers do not occur, and no workers 

 seem to act in the capacity of soldiers or scouts more than others. 

 As previously noted, the species was first described as Hypoclinea 

 humilis by Dr. G. Mayr, in 18G8, from workers collected m 1866 near 

 Buenos Aires in Argentina, the original description appearmg in the 

 Annuario della Societa dei Naturalisti di Modena, volume 3, page 

 164. Following is Mayr's description of the species kindly fur- 

 nished by Dr. W. M. Wheeler, of the Bussey Institution, Harvard 

 University, from the original edition: 



Operia: Long. 2.6 mm. Sordido ferruginea, micans, mandibularum parte apicali 

 flavescenti, abdomine nigrofusco, tarsis et nonnunquam tibiis testaceis; microscopice 

 adpresse pubescens; absque pilis abstantibus; subtilissime coriaceo-rugulosa, mandi- 

 bulis nitidis sublaevigatis punctis nonnullis; clypeus margine antico late baud pro- 

 funda emarginatus; thorax inter mesonotom et metanotum paulo et distincte con- 

 strictus, pronoto fornicato, mesonoto longitrorsum recto, transversim convexo, meta- 

 noto inermi longitrorsum fornicato, pronoto paulo altiori; petioli squama compressa 

 rotundata. 



At the request of the senior author. Dr. Wheeler prepared the fol- 

 lowing redescription of the worker, and descriptions of the queen 

 and male, thus making a complete and comprehensive description 

 of the species: 



Iridomyrmex humilis Mayr. 



Worker: Length 2.2-2.6 mm. 



Head oval, broader behind than in front, with its posterior margin slightly concave 

 in the middle. Eyes flattened, in front of the middle of the head. Mandibles with 

 two larger apical and several minute basal teeth. Clypeus short, convex in the mid- 

 dle, with broadly excised anterior margin. Frontal area and groove present but 

 rather indistinct. Antennal scapes extending about one-fourth their length beyond 

 the posterior corners of the head. Joints 1-5 and the terminal joint of the funiculus 

 distinctly longer than broad; remaining joints nearly as broad as long. Thorax slen- 

 der, narrower than the head; broadest through the pronotum which is convex, rounded 

 and nearly as long as broad. Mcsonotum nearly as long as the pronotum, sloping, 

 laterally compressed, in profile evenly continuing the contour of the pronotum. Me- 



1 An undetermined species of Iridomyrmex, apparently introduced, has been found by Dr. W. M. Wheeler 

 In a greenhouse at Boston, Mass. 



