-1 A . ('(tnadi'.ni Arctic Expedition, 1913-18 



middle of the inner nr.irgin. I'nguiculus represented only by a toothlike rudi- 

 ment. Tenent hair single, unknohhed. Kami of tenaculum quadridentate. 

 Furcuhi very long, extending as far as the first pair of legs, clearly appended to 

 the fourth al)domin;d segment. Manubrium short. Dentes long, strongly 

 bowed outward, apically convergent, with an obsolete transverse suture two- 

 fifths from the base, and with the tubercles of the distal third arranged in trans- 

 verse rings. Mucrones (figs. 2, 3) three-fifths as long as hind ungues, with outer 

 and inner lamella', and with a prominent dorsal rounded-triangular basal lobe. 

 Anal spines absent. Body clothing of few minute curving setae; dens with 12 

 t-.i 17 long curving dorsal sehr, most of which are in two longitudinal series. 

 Integument tuberculate. Length, 1.3 mm. 



I'otlum a<iuntic(i; one of the most abundant collembolans in Europe and 

 North America, occurs on the surface of standing water on the margins of ponds 

 and streams, having special structural adaptations for a ssmi-aquatic life. It 

 swarms on vegetation or rubbish along the shore, and at times is blown against 

 the shore in masses of enormous numbers. This species often appears in fresh- 

 water aquaria, and is essentially a fresh-water species, though it has been found 

 occasionally in pools of brackish water on the seashore. 



The species has been recorded from Siberia. From Canada, I have speci- 

 mens taken at Arnprior, Ont., May 19, 19i7, by Mr. Charles Macnamara. 



(Ireat numbers on ponds, Demarcation point, Alaska, May 16, 1914; 

 abundant, large and small, at Bernard harbour, Dolphin and Union strait, 

 Northwest Territories, June 25, 1915. F. Johansen. 



Achorutes tullbergi Schaffer. 



Plate 1, figs. 4-10; plate 2, fig. 11. 



Achorutes dubin* Tullberg, 1876. Uzel, 1890. Schott, 1894. Dalla Torre, 

 1895. Schaffer, 1896. Skorikow, 1900. 



Achorutes dubius, var. concolor Carpenter, 1900. 



Achorutes tullbergi Schaffer, 1900a. 



AchorutcK tullbergi, var. concolor Schaffer, 1900a. Wahlgren, H)()7. - 



, nm>. 



Pigmented with irregular patches of dark blue pigment (typical form) or 

 uniformly pigmented (var. concolor). Eyes (fig. 4) eight on each side. Postan- 

 tennal organs (fig. 1) with four (sometimes five) peripheral tubercles. Antenna- 

 shorter than the head, with segments rs 6:7:9:9 in relative lengths. Sense organ 

 of third antennal segment as in fig. 5. Ungues (fig. 6) stout, slightly curving: 

 inner margin unidentate one third from apex. Unguiculi with setaceously 

 prolonged outer margin and with the basal lamella suboblong on the second and 

 third pairs of feet. Tenent hairs knobbed; 2,3,3, as a rule; occasionally 3,3.3. 

 or 1,3,3. Mucrones (figs. 7-'.)) one-third dentes in length, apically rounded, with 

 narrow outer lamella. Kami of tenaculum quadridentate. Anal spines (figs. 

 10, 11) two, half as long as hind ungues. arcuate, on prominent contiguous 

 papillae, ('lothing of sparse short curving setuN with longer seta' on the 



rior part of the abdomen. Length, 2 mm. 



The specimens collected by the Kxpedition belong to the variety roncolor 

 Carp., which has been taken hitherto in Fran/ .)< set' Land, Kllesmcre land, 

 Bohemia and Massachusetts. The typical form of the species has been reported 

 from Xova Zeinbla, Spitsbergen and Siberia. 



Several specimens on ponds and from rotten driftwood, Bernard harbour, 

 Northwest Territories, May, 2f>, l!)l(i, June IS, 1<), l<)i:>; also several under 

 driftwood. Demarcation point, Alaska, May Hi, I'M L F. Johansen. 



