COLLEMBOLA OF THE FAMILY ISOTOMIDAE 87 



Illinois: Homer, April IG. Urbana, March 11, 13, 21. 



Canada: Arnprior, Ontario, January 4, 10, March, April 24, November, Decem- 

 ber 19, 25. 



Subgenus Isotoma Borner 



Isotoma Borner, 1906, p. 171. — Linnaniemi, 1912, p. 138. — Handschin, 1924a, 

 p. 111. 



Subgenotype. — Isotoma viridis Bourlet. 



KEY TO SPECIES OF SUBGENUS ISOTOMA 



1. Mucroues lamellate, quadridentate 2 



Mucrones noiilamellate, tridentate or quadridentate 3 



2. Last three antennal segments ahnost equal in length. Lateral 



teeth of unguis dentate or fringed distally. Anal valves con- 

 spicuous, subtriangular subaequalis (p. 107) 



Last three antennal segments uneciual in length. Lateral teeth 



of unguis entire. Anal valves not conspicuous gelida (p. 106) 



3. Mucrones tridentate 4 



Mucrones quadridentate (except a tridentate form of olivacea 



grisea) 11 



4. Large species (maximum length, 6 mm). Unguis with two 



strong inner teeth and with parallel basal folds 5 



Small species (maximum length, 1.5 mm). Claws usually un- 



toothed. Unguis without basal folds 6 



5. Teeth of mucro subequal, hooked, the two proximal teeth 



opposite each other in lateral aspect (pi. 38, fig. 437) viridis (p. 109) 



Teeth of mucro unequal, the two proximal teeth not opposite 



each other (pi. 38, fig. 445) subviridis (p. 115) 



6. Postantennal organs present 7 



Postantennal organs absent 10 



7. Eyes eight on each side 8 



Eyes four on each side eiinotabilis (p. 92) 



8. Unguis and unguiculus toothed. Postantennal organ elongate, 



narrow, in length five to seven times the diameter of an 



eye difficilis (p. 89) 



Unguis and unguiculus untoothed. Postantennal organ oval, 



not more than twice as long as the diameter of an eye 9 



9. Antennae in foveae, and strongly telescopic. Anal lobes con- 



spicuous, subtriangular niarissa (p. 89) 



Antennae not in foveae, not telescopic. Anal lobes not con- 

 spicuous trispinata (p. 91) 



10. Eye spots and corneas absent. Fourth antennal segment with 



conspicuous sensory cones minor (p. 94) 



Eye spots present but corneae absent. Fourth antennal 



sensory cones absent finitima (p. 93) 



11. Apical tooth of mucro minute, at the base of the anteapical; 



the three large teeth subequal, hooked; the two proximal 



teeth opposite each other viridis catena (p. 112) 



Apical tooth of mucro well developed; the three remaining teeth 



varying in size, form, and position 12 



12. Purple or blue, sometimes blackish. Legs and furcula ^^■hitish, 



yellowish, or brownish throughout, or purplish, basally; in 



nigrifrons, tibiotarsi purple apically 13 



Coloration various, but not as above; usually olivaceous, 



yellowish, gray, or white 16 



