COLLEMBOLA OF THE FAMILY ISOTOMIDAE 23 



"Furcula [fig. 48] short, not reaching to ventral tube; insertion at 

 junction of fourth and fifth abdominal segments. Manubrium stout 

 and thick. Dentes straight, not tapering greatly toward distal end, 

 irregularly serrulate along greater part of lower [dorsal] edge, upper 

 edge with a few stout, scattered hairs. IVIucrones and dentes together 

 about as long as the manubrium. Mucrones [fig. 49] long and narrow, 

 tridenticulate, the distal tooth almost straight, the ante-distal tooth 

 close to, and at right angles to it; proximal tooth smaller and set 

 about the middle of the mucrones, pointing slightly distal-wards. 

 Each tibia bears one long simple hair in the position of a tenent hair. 

 The claws are unarmed. 



"* * * Length, three-fourths millimetre" (Guthrie). 



Remarks. — I have seen two of the cotypes of this species, which 

 were loaned to me by Prof. H. F. Nachtrieb. Owing to the fact that 

 these specimens were mounted in balsam, the unpigmented structures 

 were almost invisible. It could be seen, however, that the last three 

 abdominal segments are ankylosed, putting this species into the genus 

 Folsomia. Faint traces of sutures between the united segments were 

 distinguishable. 



Though this species is much Uke Proisotoma minuta (Tullberg) , as 

 Linnaniemi (1912) observed, it is nevertheless distinct, and forms a 

 link between Folsomia and Proisotoma. 



Guthrie says: 



This species probably occurs more abundantly than its numbers in my collec- 

 tion would show, its minute size and light gray color lending a mimicry which 

 shields it from all but the most careful observation. It seldom jumps, seeming 

 averse to that mode of motion, but moves about uneasily when its hiding places 

 are exposed to the sunlight. I have taken it in the greenhouse of the University, 

 under moist boxes and flower pots, where it usually lived among the faeces of a 

 certain small millipede, though possibly this cooccurrence was purely accidental. 

 Out of doors it is sometimes met with under stones and damp boards, usually 

 where there is a slight layer of thin, slimy mud. Not uncommonly it is taken with 

 /. bidenticula [elo7igaia MacGillivray], the light-colored young of which it greatly 

 resembles until one observes it with a compound lens. 



Distribution. — Recorded as follows: 



Minnesota: Minneapolis, August, September, J. E. Guthrie (University of 

 Minnesota) . 



FOLSOMIA SEXOCULATA (Tullberg) 



Plate 5, Figures 50, 51 



Isotoma sexoculata Tullberg, 1871, p. 152; 1872, p. 48. — Schott, 1894, p. 74. — 

 Lie-Pettersen, 1896, p. 18; 1907, p. 61.— Schaffer, 1896, p. 183.— 

 Wahlgren, 1900a, p. 367; 1906b, p. 255.— Carpenter and Evans, 1904, 

 p. 216. 



Isotoma (Folsomia) sexoculata Axelson, 1905b, p. 29. 



Folsomia sexoculata Linnaniemi (Axelson), 1911, p. 14; 1912, p. 109. — Bartho- 

 lin, 1916, p. 168. — Carpenter and Phillips, 1922, p. 14. — Handschin, 

 1924a, p. 110; 1924b, p. 85; 1928c, p. 127; 1929, p. 57. 



