COLLEMBOLA OF THE FAMILY ISOTOMIDAE 11 



three posterior eyes in a group apart from the five anterior. Post- 

 antennal organ (pL 1, fig. 2) narrowly elliptical, four times as long as 

 the diameter of an adjacent eye, often with a constriction near the 

 middle. Antennae shorter than the head (as 10:13); segments in 

 relative lengths about as 9:13:10:19 or 17:24:23:38. Sense organ of 

 third antennal segment (pi. 1, fig. 3) in an oblique groove, with a 

 pair of oblique, basally bent sense rods, subtended by a thick chitinous 

 ridge, and covered with an integumentary fold. Fourth antennal 

 segment with curving slender olfactory setae. Unguis (pi. 1, fig. 4) 

 stout, untoothed. Unguiculus extending one-half to three-fifths as 

 far as the unguis, lanceolate, acuminate. Clavate tenent hairs two, 

 extending as far as, or farther than, the unguis. Femur with a single 

 long clavate hair (pi. 1, fig. 1). Second, third, and fourth abdominal 

 segments subequal in length dorsally. Anus ventral. Genital and 

 anal segments ankylosed, the former bearing two pairs of spines 

 (pi. 1, figs. 5, 6). Posterior spines a httle longer than hind ungues, 

 feebly curving, on stout papillae almost half as long as the spines. 

 Anterior spines similar to the posterior, but a little shorter. Ano- 

 genital segment with many long stift' hairs, many of which extend 

 backward beyond the end of the abdomen and are often apically 

 bent and minutely clavate. Furcula quite short, appended to the 

 fourth abdominal segment and extending to the posterior margin of 

 the third abdominal segment. Manubrium stout, two to two and 

 one-half times as long as the mucrodentes, with several pairs of dorsal 

 setae (pi. 1, fig. 7). Mucro and dens confluent. Mucrodentes con- 

 vergent, in form as in plate 1, figure 8, each with three setae. Rami 

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

 General clothing (pi. 1, fig. 9) of short equal curving simple setae 

 across the middle of the segment, with a transverse row of long erect 

 simple sensory setae. Cuticula not tuberculate, but reticulate. 

 Length, 2 mm. 



Remarks. — According to Linnaniemi (1912) the rami of the tenac- 

 ulum are tridentate, sometimes bidentate; and the corpus bears at 

 times two setae. He says that in Finland T. wahlgreni lives under 

 moss and lichens, as well as under stones, on the rocky summits of 

 the mountains, where it may almost always be found, not infre- 

 quently in considerable numbers. Sometimes it can be taken also 

 on pools of water. It has made its appearance early in summer, 

 before the snows have melted on the mountaintops. Common as 

 the species is on the summits of the mountains, it is seldom found in 

 the timber region, but oftener, however, in the subalpine zone. 



Distribution. — T. wahlgreni, which has been reported from Norway, 

 Sweden, Finland (north of the Arctic Circle), Spitsbergen, Bear 

 Island, Greenland, and Northwest Territories, is essentially arctic or 

 subarctic in distribution. 



