SYSTEMATIC POSITION. 27 
The subfamily Dolichoderinse contains six North American genera : 
Dolichoderus (Hypoclinea), Forelius, Tapinoma, Dorymyrmex, Lio- 
metopum, and Iridomyrmex. Iridomyrmex is essentially tropical in 
its distribution and only two species are 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 humilis 
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 1868, from workers collected in 1866 near 
Buenos Aires in Argentina, the original description appearing 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. Sordide ferruginea, micans, mandibularum parte apicali 
fiavescenti, abdomine nigrofusco, tarsis et nonnimquam tibiis testaceis; microscopice 
adpresse pubescens; absque pilis abstantibus; sub tilissime coriaceo-rugulosa, mandi- 
bulis nitidis sublaevigatis punctis nonnullis; clypeus margine antico late hand pro- 
funde emarginatus; thorax inter mesonotom et metanotum paulo et distincte eon- 
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. Mesonotum 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. 
