No. 432.] FORMICA CINEREA MAYR. 951 
These peculiar hummock formicaries occupy a zone on either 
side of the stream midway between the dryer and more boggy 
portions of the meadow, although a few of them reach quite to 
the edge of the stream and are even perforated by the burrows 
of frogs. The nests are so numerous as to be often within a 
meter’s distance of one another. Along the outer edges of 
these zones, and mingled with the dryer cinerea nests, there are 
occasional nests of F. subsericea of precisely the same structure. 
The main zone of this species, however, lies on higher ground, 
where the hummock nests are replaced by true mound nests 
entirely constructed by the ants.! 
There were some slight variations in size and coloration 
among the F. cinerea found in different nests in this locality, 
but these are all comparable to similar variations in European 
specimens. On the whole, the specimens from Illinois have 
the ground color of the head and thorax more or less reddish 
like the Californian and Austrian specimens. All the indi- 
viduals examined have a number of hairs on the lower surface 
of the head. According to Emery this is the distinguishing 
trait of cinerea among all the European Formicidz. In the 
United States F. schaufusst and F. subpolita and its varieties 
agree with cinerea in possessing such hairs, but they may be 
1 As Father Muckermann has shown in a recent paper (The Structure of the 
Nests of Some North American Species of Formica, Psyche, June, 1902, pp. 355- 
360), F. subsericea makes nests of at least four different styles: sm mall flat mound- 
as those recorded by Father Muckermann for obscuripes. 
nection that, like Father Muckermann, I do not altogether agree with Forel, who 
believes that the American are inferior to the Euro ilding. 
parts of the United States, to the species of assess and Ischnomyrmex 
in the West and d and to the es of Lasius (LZ. aphidicola, 
DUM and interjectus) in Illinois. During the men summer I saw near Rockford 
a dom ped formicary of Z. interjectus 1.5 meters in diameter at the base and 
60 centimeters high, and I have seen many nests of n and the other yellow 
species of Lasius that were fully one-half to two-thirds as 
