COLLEMBOLA OF THE FAMILY ISOTOMIDAE 9 



have many dorsal crenulations — rarely dorsal tubercles. Mu- 

 crones lamellate or not, commonly bidentate or tridentate. 

 Tibiotarsus often with a distal subsegment. Unguiculus with 

 a pair of inner lamellae in some species. Tenent hairs present 

 or absent. Clothing of simple setae, usually very short. In- 

 tegument almost always smooth, but tuberculate or reticulate 

 in a few species 7 



Fourth abdominal tergite usually shorter than the third, the two 

 sometimes subequal. Third urotergite ventrolaterally pro- 

 longed backward (pi. 31, fig. 358; pi. 38, fig. 441). Paratergite 

 of the fourth abdominal segment always united to the tergite of 

 the genital segment, or the two ankylosed without suture 

 (pi. 31, fig. 358; pi. 38, fig. 441). When the furcula is 

 extended, the membrane between the paratergites of the third 

 and fourth abdominal segments is exposed (pi. 38, fig. 441). 

 Genital and anal segments rarely ankylosed. Furcula long, 

 almost always extending to the ventral tube. Manubrium 

 much shorter than dentes, with many ventral setae. Dentes 

 long, slender, tapering, dorsally with very many transverse 

 folds or crenulations. Mucrones lamellate in a few species, 

 tridentate or quadridentate. Tenaculum with many ventral 

 setae. Tibiotarsus without a distal subsegment. Tenent 

 hairs present or absent. Clothing of relatively long setae, the 

 largest of which are not infrequently unilaterally serrate or 

 branched. Integument smooth 10 



Body segments bulging, with deep intersegmental constrictions. 

 Sclerites weakly chitinized. Terga (except genital and anal) 

 not imbricate, without well-developed intersegmental mem- 

 branes. Pronotum not greatly reduced, pigmented and tuber- 

 culate. Third urotergite simple. Genital and anal segments 

 not ankylosed. Furcula extending almost or quite to the 

 ventral tube. Manubrium slightly longer or shorter than 

 dentes, naked ventrally. Dentes stout, subcylindrical, tuber- 

 culate dorsally. Mucrones bidentate, bilamellate. Tibiotar- 

 sus with a distal subsegment. Unguiculus with a pair of inner 

 lamellae. Tenent hairs present or absent. Integument 

 tuberculate. Pigment dark blue Quthriella (p. 33) 



Body segments not bulging, without deep intersegmental con- 

 strictions. Sclerites more strongly chitinized. Terga imbri- 

 cate, with evident intersegmental membranes. Pronotum 

 pigmented or not, not tuberculate. Integument rarely tuber- 

 culate 8 



Outer lamella of unguiculus absent. Hind femur with a thornlike 

 process. Corpus of tenaculum with a large anterior accessory 

 lobe. Fourth antennal segment relatively short; shorter than 

 to slightly longer than the third. Bothriotricha present- Archisotoma (p. 66) 



Outer lamella of unguiculus present. Hind femur without a 

 thornlike process. Corpus without an accessory lobe. Fourth 

 antennal segment relatively long. Bothriotricha absent 9 



Unguis with a pair of strong lateral teeth connected by a basal 

 membrane, or tunica. Dentes tuberculate dorsally, with a 

 strong subapical seta that extends beyond the mucro. Third 

 and fourth urotergites subequal in length. Genital and anal 

 segments ankylosed. Furcula attaining the ventral tube. 

 Manubrium with many ventral setae Agrenia (p. 68) 



