1955] 
Wilson and Broivn — Formica 
109 
we have been unable to find reliable and convincing char- 
acters marking the worker caste of these three forms. 
We are keenly aware that lack of material may have 
caused us to overlook other full but more or less cryptic 
species. 
The original and present goals of this study are the 
elimination through synonymy of those names which can- 
not be supported by all available evidence, correction of 
certain inconsistencies in previous revisions (see literature 
cited at end of paper), and construction of a new key 
based on the present revision. After the majority of the 
work had been completed, however, another important 
consideration arose. 
It had 'become apparent early in the task that Rapti- 
formica included two species-groups, termed by us respec- 
tively “sanguinea complex” and “ obtusopilosa complex.” 
The sanguinea complex is distinguished by the follow- 
ing assemblage of characters: 
(1) The workers of all of the species usually have the 
gasters black and the remainder of the body red, except 
F. parcipappa, which is concolorous reddish yellow. 
(2) The workers average large in size for Formica 
are robust, and have a well-defined metathorax. 
(3) The propodeum is short, with a well-defined angle, 
and the petiolar scale is high and thin. 
(4) The gastric pubescence is dense and the body pilosity 
generally sparse. Hairs are never present on the dorsal 
face of the propodeum anterior to the propodeal angle. 
(5) The sculpture is generally opaque, or at most rather 
weakly shining. 
(6) The male has relatively broad parameres and a 
subgenital plate of a particular conformation (figs. 3, 5). 
(7) All of the species take slaves, at least facultatively, 
except F. parcipappa, which is known only from limited 
cabinet material. 
(8) The complex as a whole prefers mesic habitats. 
