COLLEMBOLA OF THE FAMILY ISOTOMIDAE 27 



FOLSOMIA DIPLOPHTHALMA (Axelson) 



Plate 6. Figures 59-67 



Isotoma diplophthalma Axelson, 1902, p. 106. 



Folsomia quadriocidata Tullberg, var. diplophthalma Axelson, 1907, p. 30; 



1909, p. 13. — CoLLiNGE and Shoebotham, 1910, p. 110. 

 Isotoma binoculata Collinge and Shoebotham, 1909, p. 88. 

 Folsomia diplophthalma Linnaniemi (Axelson), 1911, p. 13; 1912, p. 113. — 



Wahlgren, 1919, p. 745.— ScHOTT, 1923, p. 11.— Remy, 1928, p. 66.— 



Handschin, 1929, p. 58. 

 Isotoma (Folsomia) diplophthalma Folsom, 1919b, p. 276. 



Description. — Elongate. Wliite, with a slight amount of pigment 

 in the form of scattered minute blackish dots; or without pigment 

 except that of the eyes; or pale gray with patches of pigment irregular 

 in size and distribution. Eyes (pi. 6, figs. 59, 60) one on each side, 

 appearing as round black spots. Postantennal organ (pi. 6, figs. 

 59, 60) close to the eye, large, four to seven times as long as the 

 diameter of the eye, subelliptical, often but not always constricted 

 near the middle, \A^th thick chitinous wall, xintennae slightly longer 

 than the head, with segments in relative lengths about as 4:9:8:16. 

 Sense organ of third antennal segment (pi. 6, fig. 61) with a pair of 

 slender feebly curving rods and a chitinous ridge. Fourth antennal 

 segment with terminal tubercle, subapical papilla, and several 

 olfactory setae, somewhat shorter and stouter than the other setae. 

 Body subcylindrical, abdomen but slightly dilated. Unguis (pi. 6, 

 figs. 62, 63) simple, without lateral or inner teeth. Unguiculus 

 extending half as far as the unguis (first pair) or almost two-thirds 

 as far (thhd pair), lanceolate, untoothed. Tenent hairs absent. 

 Fourth, fifth, and sixth abdominal segments ankylosed dorsally; 

 either .without sutures or, in some instances, with a suture between 

 the fourth and fifth. Anus ventrocaudal. Fiu'cula appended to 

 the fourth abdominal segment, short, extending not quite to the 

 posterior edge of the second abdominal segment. Manubrium stout, 

 longer than dentes. Manubrium: dens :mucro about as 48:37:10. 

 Dens (pi. 6, fig. 64) stout, with a few minute dorsal crenulations 

 near the middle, and a long erect dorsal proximal seta. Between 

 the bases of the dens are two pairs of strong chitinous hooks (pi. 6, 

 figs. 64, 65). Mucro (pi. 6, fig. 66) three-fifths as long as hind 

 unguis, bidentate; apical tooth slightly hooked; anteapical tooth 

 usually larger than the first tooth, suberect or feebly hooked. Rami 

 of tenaculum quadridentate; corpus with a single stout curving seta. 

 Clothing (pi. 6, fig. 67) of dense short stiff simple setae, absent on 

 the anterior and posterior parts of most of the body segments. 

 Sensory setae long, outstanding, simple. Length, 1.3 mm. 



Remarks. — All the specimens that I have seen have been white, 

 with little pigment at most, though Linnaniemi (1912) mentions also 



