344 Bulletin American Museum of Natural History. [Vol. XXII, 



also the apical half of each tibia. In some specimens the pleurge also are more 

 or less infuscated. 



Described from 25 workers taken from a small colony under a 

 stone on the wall of the Grand Canon at an altitude of about 5500 feet 

 and 2 workers taken on the rim in the Kohonino Forest (7000 feet) 

 about three miles west of the Bright Angel Hotel. 



This species seems to belong to the Formica rufa group although 

 certain characters ally it with F. fusca. At first sight it resembles 

 rather deeply colored specimens of the var. neoclara Emery of the 

 latter species, but it differs from this and all the other North American 

 FormiccB known to me in the very low and flat thorax and the length 

 of the mesoepinotal constriction. In these respects it approaches the 

 forms of the pallide-fulva group, but the surface of the body is sub- 

 opaque as in the smaller species allied to F. rufa. It will be impossible 

 to assign F. moki to a precise position in the genus till the female is 

 discovered . 



24. Formica fusca Linn. var. argentata Wheeler. — Workers from 

 one small colony of this subboreal variety were taken on the rim of 

 the cafion at an elevation of a little over 7000 feet. No sharp line 

 can be drawn between argentata and var. subsericea Say although it is 

 easy to distinguish extreme specimens of the two varieties. F. 

 argentata is more abundant in the western States at considerable 

 elevations, subsericea in the eastern and middle States at lower 

 altitudes. 



25. Formica fusca Linn. var. gnava Buckley. — Numerous small 

 colonies were found nesting in the grass and among the willows at 

 the Indian Garden. The workers of this variety, which is quite 

 distinct from the var. neorufibarbis Emery, in having the gaster much 

 more pubescent and therefore more opaque, are indistinguishable 

 from specimens taken from larger colonies in similar situations in 

 other parts of Arizona (Ash Fork and Prescott and in Texas [Austin, 

 New Braunfels, San Angelo, Fort Davis, Langtry, etc.]). This ant 

 always prefers the moist shady banks of streams and is never found in 

 the dry open country. 



26. Formica fusca Linn. var. neorufibarbis Emery. — 'This variety, 

 which is rare on the rim of the canon at an elevation of 7000 feet, is 

 similar in coloration and sculpture to F. subpolita Mayr, but lacks 

 the erect hairs on the lower surface of the head. It belongs to the 

 Canadian and Hudsonian zones and in the United States seems rarely 

 to descend below 7000 or 8000 feet. In Colorado I have taken it 

 only in the higher cafions and near timber-line on the mountains. 



