COLLEMBOLA OF THE FAMILY ISOTOMIDAE 33 



Folsomia nivalis is closely related to F. Jimetaria, from which it is 

 distinguished chiefly by the long narrow postantennal organs, the 

 tooth of the unguis, and the shorter dentes. 



Distribution. — Recorded as follows: 

 Maine: Brunswick, September 10, under bark, common, A. S. Packard (Museum 

 of Comparative Zoology). Orono, January, several hundred in a cellar 

 in decaying beets; May, F. L. Harvey. April, Edith M. Patch (J. E. 

 Guthrie) . 

 New York: New York City, July, F. Silvestri. 



Genus GUTHRIELLA Borner 



Isotoma Guthrie, 1903, p. 72. 

 Guthriella Borner, 1906, p. 172. 



Genotype — Isotoma muskegis Guthrie. 



Body and appendages robust. Body segments bulging, with deep 

 intersegmental constrictions. Sclerites weakly chitinized, not sharply 

 demarcated from one another. Tergites not imbricate; without well- 

 developed intersegmental membranes. Prothorax not greatly 

 reduced, pigmented and tuberculate, not membranous. Abdominal 

 segments without ankylosis. Fourth abdominal tergite longer than 

 the third. Third uro tergite simple in form; the ventrolateral region 

 not prolonged posteriorly. Anus not directed ventrally. Eyes 16 

 (in the three known species). Postantennal organs present, simple. 

 Fourth antennal segment with olfactory setae and a terminal hemi- 

 spherical sensory tubercle. Tibiotarsus with a distal subsegment. 

 Unguis without lateral teeth. Unguiculus with a pair of inner 

 lamellae. Tenent hau's present or absent. Ventral tube with a pair 

 of rounded vesicles. Furcula long. Manubrium naked ventrally. 

 Dentes stout, subcylindrical, not tapering. Mucrones bidentate, 

 with equal inner and outer dorsal lamellae. Clothing of short equal 

 curving simple setae; long sensory setae absent. Pigment dark blue 

 (in the known species). Integument tuberculate. 



The male of the species muskegis exhibits secondary sexual dimor- 

 phism. 



On each side of the base of the furcula, between the fourth and 

 fifth urotergites, there is an accessory sclerite (pi. 9, fig. 89), rounded 

 ventrally, pigmented, and tuberculate. This sclerite occurs in all 

 three species of this genus and in a few other generalized species of 

 Isotomidae, but it is absent in the more specialized forms. 



KEY TO SPECIES OF GUTHRIELLA 



1. Furcula extending to the ventral tube. Unguis with an inner 

 tooth. Postantennal organ with a notch in the middle of 

 the anterior margin muskegis (p. 36) 



Furcula not extending to the ventral tube. Unguis untoothed. 



Postantennal organ without a notch in the anterior margin 2 



