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



sylvania, described nearly thirty years ago by McCook.^ With the 

 aid of my assistant, Mr. Roy E. Miner, I measured eleven of the 

 largest inounds and record their height, transverse diameter through 

 the base and OA^er the summit and the circumference in meters and 

 in feet, in the following table: 



The average height of these mounds is .78 m. (2 ft. 6.5 in.) with a 

 basal diameter of 2.40 m. (7 ft. 10 in.), a convex diameter of 2.77 m. 

 (g ft. 5 in.) and a circumference of 7.55 m. (24 ft. 7.9 in.). They 

 exhibit considerable differences in shape, some being more pointed 

 or conical, others more depressed and rounded. Although unusually 

 well developed, none of these hills reaches the dimensions of one 

 measured by McCook (/. c, p. 255). This, the largest on record, was 

 1.07 m. (3 ft. 6 in.) in height, 7.34 m. (24 ft.) in diameter over the 

 summit, and 17.75 ^"^^ (S^ ^^O i^ circumference. 



The mounds of F. exsectoides undoubtedly answer the same purpose 

 as those of F. rufa in Europe and certain of its varieties in this countr}^ 

 As Forel has shown, these accumulations of detritus serve as incu- 

 bators for the brood, since their temperature during the day is, of 

 course, much higher than that of the underground portions of the 

 nests. Unlike the mounds of F. rufa, however, those of F. exsec- 

 toides consist very largely of earth and only to a very limited extent of 

 vegetable detritus and pebbles. McCook is certainly in error when he 

 writes (1. c, p. 270) that "every hill furnishes a fair measure of the 

 extent of the underground system of galleries connected therewith; 

 for it is reasonably certain that the entire bulk of soil in each mound 

 has been excavated and brought from the galleries beneath the sur- 



1 Mound-building Ants of the Alleghenies. Trans. Am. Entom. Soc, VI, 1877, pp. 2^3-196, 

 pU. ii-vi, T3 text-figs. 



