COLLEMBOLA OF THE FAMILY ISOTOMIDAE 79 



1901b, p. 153.— Krausbauer, 1902, p. 41.— Agren, 1903, p. 139; 1904, 



p. 17.— Guthrie, 1903, p. 67. — Linnaniemi (Axelson), 1907, p. 30; 



1911, p. 15.— ScHiLLE, 1906, p. 8.— Brown, 1918, p. 186; 1919, p. 64; 1923, 



p. 262.— Denis, 1924a, p. 260. 

 Isoioma dubia Reuter, 1895, p. 27. 

 Isotoma deterininata MacGillivray, 1896, p. 54. 

 Isoioma parva MacGillivray, 1896, p. 50. 

 Isotoma longidens Schaffer, 1896, p. 188. 

 Isotoma monstrosa Schaffeu, 1896, p. 189. 

 Isoioma inopinata Axelson, 1902, p. 108. 

 Isoioma (Verlagopus) sensibilis Linnaniemi, 1912, p. 143. — Handschin, 1919, 



p. 76.— Stach, 1921, p. 161.— ScHOTT, 1923, p. 11.— Womersley, 1924a, 



p. 32; 1925, p. 219. 

 Isotoma (Pseudisotoma) sensibilis Handschin, 1924a, p. 111. 

 Pseudisoloma sensibilis Handschin, 1924b, p. 85; 1929, p. 64. — Remy, 1928, p. 65. 



Description. — Bluish gray, greenish, clear blue, or blackish blue. 

 A common form of the species under loose bark of dead trees 

 (MacGillivray's determinata) is green, marked with blackish; with 

 the ground color white; and, in individuals that are not too heavily 

 pigmented, with minute round wliite spots distributed abundantly 

 and uniformly throughout the green areas. Large irregular white 

 spots occur dorsally on the head, mesonotum, metanotum, and the 

 first five abdominal segments. A /\ -shaped black marking extends 

 forward from the eyes. An irregular median black spot occurs mid- 

 way between the eyes and the posterior border of the head. Second 

 and third thoracic, and the first four or five abdominal segments 

 bordered posteriorly with black, wliich extends also along the lateral 

 margins of the tergites, particularly the mesonotum and metanotum. 

 Sternum, legs, and furcula white; or manubrium pigmented slightly. 

 Antennae pale green proximally, dull bluish green distally; or bluish 

 throughout: first two segments green, ringed with black apically; 

 last two segments green, mottled with blue. Other forms of the 

 species have blue, instead of green, pigment. Young individuals 

 may be almost white. Eyes (pi. 27, fig. 296) eight on each side; 

 the two inner proximal eyes of each group smaller than the others. 

 Postantennal organ (pi. 27, fig. 296) broadly elliptical, oval or sub- 

 ovate, varying from a little shorter than, to one and one-half times 

 as long as, the diameter of an adjacent eye. Antennae a little 

 longer than the head, stout: third segment slightly shorter to slightly 

 longer than the second; fourth, one and one-half to two times as long 

 as the tliird. Sense organ of third antennal segment with a pair of 

 stout curving rods under an integumentary fold, and subtended by a 

 chitinous ridge. Fourth antennal segment without special olfactory 

 setae. Third abdominal segment subequal to fourth or a little longer 

 (as 15:13). Genital and anal segments ankylosed. Unguis (pi. 27, 

 fig. 297) with a small inner tooth one-fourth from the apex (some- 

 times absent, however) and a pair of small lateral teeth. Unguiculus 

 extending almost half as far as the unguis, broadly lanceolate or 



