30 BULLETIN 168, UNITED STATES NATIONAL MUSEUM 



of the postantennal organ is one-half to three-fifths the width of the 

 base of the first antcnnal segment, while in many examples from 

 Illinois (pi. 7, fig. 71) it ahnost or quite equals the basal width of 

 that segment. 



In both Europe and North America the mucrones are somewhat 

 variable in length and slenderness (pi. 7, figs. 76, 77). 



In small individuals the antennae are shorter than the head; in 

 large specimens they are longer than the head. The antennal seg- 

 ments vary greatly in relative as well as absolute lengths, according 

 to the size of the individual, and become more nearly cylindrical 

 with age. 



Rarely, the unguis bears an inner tooth. 



In some individuals an obsolete dorsal suture between the fourth 

 and fifth abdominal segments can be distinguished. 



Some of the largest individuals have two setae on the tenaculum, 

 one in front of the other. 



In specimens from Washington, D. C. (Folsom, 1902b), the postan- 

 tennal organs were ovate or oval, and the dentes were two and one- 

 half times as long as the manubrium. 



Specimens from Alaska (Folsom, 1902a) had somewhat shorter 

 antennae and stouter claws than those from Massachusetts. 



According to Borner (1901), European examples sometimes vary 

 to yellowish, and rarely show a little blackish pigment. 



Determination. — Massachusetts specimens of this species agree in 

 every essential with European examples, as Doctor Schaffer and I 

 found, through an exchange of material, many years ago. Some 

 European writers describe the postantennal organ as being long and 

 narrow, but my European specimens show all variations from long 

 and narrow to short and broad. The sensory rods of the third 

 antennal segment are slenderer in European than in North American 

 examples of the species. 



Synonymy. — MacGiUivray's (1896) description of /. manubriata 

 applies evidently to Jimetaria, and a cotype of manubriata that he 

 gave me proved to be a small individual oi Jimetaria. 



Schott (1896) was inclined to regard Packard's nivalis as this 

 species. Such is not the case, however, as I found by an examination 

 of Packard's cotypes. 



Habitat. — Folsomia jimetaria belongs to the fauna of the soil and 

 is one of our commonest species, being found among the roots of 

 plants, under damp wood, stones, or bark, in moss, and not infre- 

 quently on well water. It occurs often in flowerpots in dwelling 

 houses or greenhouses, having been brought in with the soil; and has 

 been found in caverns and in graves. 



Distribution. — In northern and middle Europe F. jimetaria is one 

 of the commonest and best known of coUembolans. It is known also 



