82 BULLETIN 168, UNITED STATES NATIONAL MUSEUM 



Head with an anteocular blue spot, often ill defined. An elongate 

 species. Eyes (pi. 27, fig. 300) eight on each side, siibeqiial. Post- 

 antennal organ (pi. 27, fig. 300) broadly elliptical, oval or ovate; 

 about twice as long as the diameter of an eye. Antennae one and 

 one-half to almost two times as long as the head; segments apically 

 or entirely purplish, in relative lengths about as 6:9:10:20. Sense 

 organ of third antenna! segment (pi. 27, fig. 301) consisting of a 

 pair of linear rods, basally curving, subtended by a chitinous ridge. 

 Mesonotum with an anteromedian rounded emargination. Unguis 

 (pi. 27, fig. 302) with an inner tootJi beyond the middle, one-third 

 from the apex, and a pair of small lateral teeth one-third from the 

 base. Unguiculus one-half to two-thirds as long as unguis, lanceo- 

 late, acuminate, unidentate on the inner margin. Knobbed tenent 

 hairs two or three on each tibiotarsus. Third abdominal segment 

 a little longer than the fourth (as 17:14). Genital and anal seg- 

 ments not ankylosed. Furcula appended to the fifth abdominal 

 segment; extending almost to, or slightly beyond, the posterior 

 margin of tlie second abdominal segment. Dentes twice as long as 

 manubrium, slender, tapering, apically convergent, dorsally crenu- 

 late. Mucrones (pi. 27, figs. 303-307) a little shorter than hind 

 unguiculi, quadridentate, with ventral margin straight to slightly 

 convex in lateral aspect; apical tooth straight to subfalcate, some- 

 times reduced; second and third teeth subequal, or the third smaller, 

 conical, suberect or feebly hooked; first three teeth in longitudinal 

 alinement; fourth tooth lateral, near the third, acute, oblique, or 

 suberect, sometimes reduced or absent (pi. 27, fig. 307). Rami of 

 tenaculum (pi. 27, fig. 308) quadridentate; corpus with six to nine 

 ventral setae. Clothing of dense short curving reclinate setae, with 

 a few long outstanding sensory setae, simple or wealdy spinulate. 

 Length, 1.6 mm. 



Remarks. — The amount of blue pigment varies greatly but increases 

 with the age of the individual as a rule. The antennae and furcula 

 increase in relative length with age; and in small individuals the former 

 may not be much longer than the head. In small individuals the 

 inner tooth of the unguis and that of the unguiculus are small or 

 absent. The common formula for the number of tenent hairs is 

 2, 3, 3; this occurring in 48 percent of the Massachusetts specimens 

 that I examined; the other formulae found being 2, 2, 2 (23 percent), 

 2, 2, 3 (23 percent), and 3, 3, 3 (6 percent). The mucrones vary 

 considerably in form, as is shown in figures 303 to 307, and many 

 mucronal variations may be found in members of the same colony. 



Two individuals, taken at Homer, 111., are unusually long — 2.7 mm. 



At one time I sent Massachusetts specimens to Dr. C. Schaffer, 

 who reported them to be the common European I. cinerea (Nicolet), 

 and in return he sent me European examples of the species, enabling 

 me to confirm his determination. 



