COLLEMBOLA OF THE FAMILY ISOTOMIDAE 29 



Folsomia fimetaria Linnaniemi (Axelson), 1907, p. 21; 1911, p. 14; 1912, p. 

 114. — CoLLiNGE, 1910, p. 9. — CoLLiNGE and Shoebotham, 1910, p. 109. — 

 Shoebotham, 1914, p. 62; 1917, p. 221.— Bartholin, 1916, p. 168.— Brown, 

 1918, p. 186.— Denis, 1921, p. 125; 1922a, p. 111.— Stack, 1921, p. 125.— 

 Handschin, 1924a, p. 110; 1924b, p. 85; 1926, p. 130; 1929, p. 58.— Womers- 

 ley, 1924a, p. 32; 1927, p. 376.— Folsom, 1927, p. 6.— Remy, 1928, p. 66. 



Folsomia fimentaria Wahlgren, 1919, p. 750. 



Description. — Wliite, slender. Eyes and ocular pigment absent. 

 Postantennal organs (pi. 7, figs. 68-71) narrowly elliptical to sub- 

 reniform, occasionally oval or ovate, typically half as long as the 

 basal width of the fii'st antennal segment, but in some individuals 

 considerably longer. Antennal base well developed. Antennae 

 longer than the head, with segments in relative lengths about as 

 3:9:8:14 or 3:7:6:9. Second antennal segment subclavate or cylin- 

 drical; third clavate; fourth elliptical to subcylindrical. Sense organ 

 of third antennal segment (pi. 7, fig. 72) with a pair of subreniform 

 or subclavate sense rods, subtended by a chitinous ridge. Fourth 

 antennal segment with terminal tubercle, subapical papilla, and 

 several long pointed olfactory setae. Unguis (pi. 7, fig. 73) slender, 

 slightly curving, untoothed. Unguiculus about half as long as 

 unguis, broadly lanceolate, acuminate, untoothed. Hind claws larger 

 than the others. Tenent hairs absent. Last three abdominal seg- 

 ments ankylosed (pi. 7, figs. 74, 75), without dorsal sutures. Ab- 

 domen rounded posteriorly. Anus ventrocaudal. Fiu-cula appended 

 to the fourth abdominal segment, extending to the posterior border 

 of the first abdominal segment or only to that of the second. Manu- 

 brium with many ventral setae in adults but only two pairs (distal) 

 in the young. Dentes almost or quite twice as long as the manu- 

 brium, gradually tapering, with very many dorsal crenulations except 

 on the proximal third. Mucrones subequal in length to hind un- 

 guiculi, bidentate (pi. 7, figs. 76, 77); apical tooth feebly curving; 

 second tooth subequal to, or larger than the first, conical, erect. 

 Rami of tenaculum (pi. 7, fig. 78) quadridentate ; corpus with a 

 single stout ventral seta. Clothing (pi. 7, fig. 79) of dense short 

 setae, absent in the intersegmental regions. Long stiff simple sensory 

 setae occur in a transverse row of six across the middle of abdominal 

 segments one to three, inclusive; about 16 such setae, much longer, 

 however, are present on the ankylosed last three abdominal seg- 

 ments ; and similar long outstanding setae occur also on the posterior 

 border of the head, mesonotum, and metanotum, on the anterior 

 border of the mesonotum, and sparingly on the legs. Maximum 

 length, 2 mm. 



Variation. — The postantennal organs vary considerably in form 

 and size, as indicated in plate 7, figures 68 to 71; both European 

 and North American specimens varying in these respects. In speci- 

 mens from Massachusetts and New Jersey (pi. 7, fig. 70), the length 



95462—37 3 



