1955] 
Wilson and Brown — Formica 
117 
beyond the dorsal margin of the pronotum seen from the 
side; in subnuda at most three or four are visible in this 
view, and usually less. 
(3) The head of sanguinea is always infuscated, and 
on the average more deeply than in subnuda, although 
there is some amount of overlap in the total variation of 
the two species. 
Despite the completely allopatric distribution of san- 
guinea and its obvious cognate relationship to subnuda, 
we are treating the two forms as distinct species. The 
reason is that they differ by at least two discontinuous 
characters, while the total morphological difference is ap- 
parently greater than that separating some of the sym- 
patric Nearctic species. Thus, in the absence of direct 
evidence concerning their status, reliance is placed on an 
arbitrary, morphological “species-standard” method in 
order to insure uniformity of treatment throughout the 
species group. 
The intermediate position of sanguinea between subnuda 
and subintegra with respect to the pilosity and clypeal 
notch characters described above may represent another 
case of the phenomenon of “character displacement” as 
recently described in the genus Lasius by Wilson (1955). 
Our interpretation would be that subnuda remains well 
segregated morphologically from subintegra because it is 
partly sympatric with it, and as a result the two species 
tend to occupy ecologically different “niches.” As a distinct 
species and the Palaearctic equivalent of subnuda, san- 
guinea has no such competitor, and therefore presumably 
converges morphologically toward subintegra in filling the 
adaptive vacuum which a companion species might other- 
wise occupy. 
We have made no attempt to treat the Palaearctic 
“varieties” of sanguinea in the present study. Most of 
these are based on color differences and do not seem on 
cursory examination to be strong candidates for species 
rank. We have included in our diagnosis of sanguinea 
varietal material from the following several localities: 
Guadarrama, Spain (C. Schramm leg.; var. flavorubra 
