102 BULLETIN 168, UNITED STATES NATIONAL MUSEUM 



Description. — Clear purple, blackish purple, or dark blue. Legs 

 and furcula wliite or yellow-ish throughout, or pigmented basally; 

 antennae purple. Body wdth many pale spots; head frequently 

 pale laterally. Postantennal organ (pi. 33, fig. 384) situated close to 

 the eyes, elliptical; equal to, or slightly longer than, the diameter 

 of an adjacent eye (as 7:6 or 10:9), with a thick wall. Eyes (pi. 33, 

 fig. 384) eight on each side, subequal (sometimes the two inner proxi- 

 mal eyes of each side smaller than the others). Antennae longer than 

 the head, wdth segments in relative lengths about as 11:15:18:30 

 or 9:14:15:29. Sense organ of third antennal as in plate 33, figure 

 385. Fourth antennal segment without special olfactory setae; 

 with three large unequal apical tubercles and a subapical depression 

 with a papilla. Unguis (pi. 33, fig. 386) curving, with a pair of lateral 

 teeth, and typically with a strong inner tooth (sometimes absent). 

 Unguiculus extending a Httle more than half as far as the unguis, 

 broadly sublanceolate, acuminate, with an inner angle-tooth, which 

 is usually evident but occasionally obscure. Tenent hairs absent; 

 instead, a long simple hair is present. Abdominal segments without 

 ankylosis. Tliird and fourth abdominal segments subequal, or third 

 slightly shorter than the fourth (as 6:7). Furcula appended to the 

 fifth abdominal segment, extending to the ventral tube. Dens two 

 and one-half times as long as the manubrium, slender, gradually 

 tapering, crenulate dorsally, the crenulations becoming gradually 

 smaller distally and disappearing far in advance of the mucro (at a 

 distance from the mucro equal to three times the length of the latter) . 

 Mucro slightly shorter than hind unguiculus, quadridentate (pi. 33, 

 fig. 387) ; apical tooth usually the longest. Anteapical tooth suberect, 

 occasionally as large as the apical tooth. Tliird and fourth teeth 

 proximal, almost opposite each other; one of them being lateral in 

 position. A subapical ventral bristle on the dens extends beyond the 

 middle of the mucro in some individuals; in others it is short. Kami 

 of tenaculum quadridentate; corpus with several (7 to 11) stout 

 ventral setae (as many as 16 in large European examples). General 

 clothing (pi. 33, fig. 388) of numerous strong, stiff or curving setae, 

 moderately long; with long stout outstanding setae, numerous and 

 bowed on the last two abdominal segments. Length, 2 mm. 



Remarks. — In European specimens the body color is sometimes more 

 or less brownish (Schaffer, Skorikow). In some of my material from 

 Canada the postantennal organ is twice as long as the diameter of an 

 eye — a variation that Linnaniemi also has found in Europe, In 

 some individuals from Canada, typical in other respects, the two 

 inner proximal eyes of each group are smaller than the others. This 

 variation occurs also in various other species of Isotoma. 



My material of this species from Canada and Greenland agrees 

 in all essentials with European descriptions of the species and with 

 specimens from Germany received from Dr. Schaffer. 



