58 PROCEEDINGS OP THE ACADEMY OF [1884. 



This characteristu; the Americaa Riifas have in common 

 with their European congeners; the F. rufa of Switzerland, for 

 example, is found as far up the Alps as the line of vegetation, 

 further progress being apparently limited by the lack of vege- 

 table growth rather than by the temperature.^ They may, there- 

 fore, be reckoned, both on this continent and Europe, as among 

 the most hardy of the ant fauna, best adapted to contend with 

 severities of cold. 



Extei~ior Architecture of Mounds. — The ant-hills in Dakota are 

 for the most part conical elevations, somewhat flattened at the 

 top (fig. 1). Some present the peculiarity of a square base, giving 

 the hill the shape of a pyramid, whose apex is rounded (fig. 2 ). Dr. 

 De Puy's measurements show heights varying from one foot and 



a half, to eight inches. 

 ,u^&Mi^^J^i^-W-'^.^:.y^kOHf, The slopes of the 



'WK/^?*'^:li^-';/.Js^^'i'^^^ sides in two cases are 



twenty-one and twen- 

 ty-three inches re- 

 spectively; two diam- 

 eters measured are 

 two feet, and one foot 

 six inches, respec- 

 tively; and one mound 

 gave a measurement 

 of ten feet around the 

 Fig. 1. Conical Mound. -Dakota. base. The mounds, 



according to Mr. Russell, average from twelve to fifteen inches 

 in height, and about eighteen inches in base diameter. They 

 are separated from each other by interspaces of from twenty to 

 sixty feet, and are scattered over the prairie in groups or " villages." 

 Dr. De Puy says that one may travel miles without seeing ant-hills, 

 and then come upon clusters of them. 



The mounds which I observed in Colorado were chiefly circular 

 elevations of earth, very much flattened at the top (fig. 3). They 

 varied greatly in size, but rarely rose to a greater height than 

 eight inches. One mound observed in South Park and figured, 

 was shaped like a stocking (fig. 4), an odd form certainl}^ and 



' Catalogue des Formicides d'' Europe, by Emory and Forel, p. 450, Mit- 

 theilungen der Schweizerischen entomologischen Gesellschaft. 



