NO. 2134. trORTH AMERICAN COLLEMBOLOUS IN.^ECT.^—FOLSOM. 485 



broad and rounded, bearing dorsally four to seven prominent acutely- 

 conical teeth, besides several or many smaller pointed teeth. Mucro 

 (figs. 47, 48) one-fourth as long as dens, inserted on inner side of apex 

 of dens, and somewhat boat-shaped; in profile, suboblong, feebly curv- 

 ing, apically refuse or emarginate. Anal spines (fig. 49) two, small, 

 conical, erect or curving slightly forward, on low, separated papillae. 

 Clothing (fig. 50) of simple setae. Maximum length, 2 mm. 



The postantennal organ rarely has five peripheral tubercles. The 

 " Nebenhocker " is round or rounded-triangular. The sense-organ 

 of the third antenna! segment is essentially the same in American 

 and European specimens (compare my fig. 45 with Absolon, '016, 

 fig. 1). The " Riechzapf chen " of the fourth antennal segment, how- 

 ever, are often longer and more curving than they appear in the figure 

 given by Absolon ('016, p. 583). The teeth of the dentes are modi- 

 fied cuticular tubercles; on the proximal side of the large teeth there 

 are often several small teeth which merge into the minute tu])ercles 

 of the integument (fig. 47). The mucro varies somewhat in form, 

 chiefly in the depth of the apical notch, which is sometimes almost 

 absent; in a few specimens I have seen the form of mucro represented 

 by Schott ('94a, pi. 7, fig. 7), but in only a few out of many hundreds 

 of specimens examined. 



Owing to the inadequacy of Fitch's original description of Podura 

 nivicola I redescribed his species in 1902. The first competent 

 description of the species was given, however, by Uzel in 1890; hence 

 his name socialis should be used instead of nivicola. 



North American specimens agree accurately with three Swedish 

 examples of socialis which were determined l)y Schott and sent to 

 me by Schaffer. 



I sent American specimens to Schaffer, who replied that his Aclio- 

 rutes spinifer was a color variety of nivicola (socialis). 



Lintner's diversice'ps is a synonym of socialis Uzel. I have studied 

 Lintner's cotypes through the kindness of Dr. E. P. Felt. 



For the loan of Guthrie's specimens of A. socialis I am indebted to 

 Prof. H. F. Nachtrieb. 



This is an abundant species in our forests in the winter and fore part of spring. At 

 any time in the winter, whenever a few days of mild weather occur, the surface of 

 the snow, often over whole acres of woodland, may bo found sprinkled more or less 

 thickly with these minute fleas, looking, at first sight, as though gunpowder had 

 been there scattered. Hollows and holes in the snow, out of which the insects are 

 unable to throw themselves readily, are often black with the multitudes which here 

 become imprisoned. The hairs which clothe their bodies enable them to float 

 buoyantly upon the surface of water without becoming wet. When the snow is 

 melting BO as to produce small rivulets coursing along the tracks of the lumberman's 

 sleigh, these snow-fleas are often observed, floating passively in its current, in such 

 numbers as to form continuous strings ; whilst the eddies and still pools gather them 

 in such myriads as to wholly hide the element beneath them. In the early spring 

 the buckets and troughs of the manufacturer of maple sugar are often thronged with 

 these insects. (Fitch.) 



