1912] Wheeler — Ants of the Genus Mynnecocystus Wesmael 173 



melliger, but such a physiological caste is still unknown in the sub- 

 species orhiceps, viendax, mimicus and seminifus and in M. lugu- 

 bris and yuma. All of these seem to be eminently predatory and 

 insectivorous. The repletes of the typical M. mexicanus and its 

 subspecies mojave have been studied by Leonard, and it is highly 

 probable that the subspecies navajo presents very similar condi- 

 tions. 



I append a table for the identification of the workers of all the 

 known species, subspecies and varieties of Myrmecocystiis with 

 some geographical and ethological notes and with descriptions of 

 the new forms. 



Table of Myrmecocystus. 



1. Mandibles 9-toothed; eyes larger; head and thorax and usually also the gaster 



yellow 2 



Mandibles 7-toothed; eyes usually smaller; color always darker, head and 

 thorax red or more or less inf uscated 5 



2. Large forms, averaging more than 5 mm 3 



Small forms, averaging less than 5 mm 4 



3. Head a,nd thorax sordid yellow, gaster brown or blackish, .mexicanus Wesmael. 

 Head, thorax and gaster pure yellow .... mexicanus var. horti-deorum MacCook. 



4. Head narrow; pronotum longerthan broad; base of epinotum very convex; erect 



hairs only on anterior surfaces of antennal scapes . . mexicanus navajo Wheeler. 



Head broader; pronotum as broad as long; base of epinotum less convex; whole 



of antennal scapes with erect hairs mexicamis mojave ^\Tieeler. 



5. Large forms, averaging more than 4 mm.; stature very variable 6 



Small forms, averaging less than 4 mm.; stature more constant 13 



6. Gaster opaque or subopaque, densely pubescent; length 7-9 mm 7 



Gaster shining, with shorter and more dilute pubescence; length 4-6 mm . . 10 



7. Hairs and pubescence grayish, the latter short, not silvery; length 8-9 mm. 



melliger Forel. 



Hairs and pubescence silvery, the latter longer; length 7-8 mm 8 



8. Head of largest workers large, orbicular melliger orhiceps ^ATieeler. 



Head of largest workers smaller, rectangular 9 



9. Erect hairs shorter and less abundant, obtuse or subobtuse 



melliger mendax Wheeler. 



Erect hairs longer, more abundant, pointed 



- melliger mendax var. comatus Wheeler. 



10. Erect hairs nearly or quite lacking on antennal 



scapes melliger mimicus var. depilis Forel. 



Erect hairs abundant on antennal scapes 11 



