10 A Canadian Arctic Expedition, 1913-18 



Isotoma palustris TuUberg, 1871, 1872, 1876.— Uzel, 1890. 



Isotoma Belfragei Paikard, 1873. — MacGillivray, 1891. 



Isotoma tricolor Packard, 1873 (part). — -MacGillivray, 1891 (part). 



Isotoma purpurascens Packard, 1873. — MacGillivray, 1891. , 



Isotoma plumbeaFacksbid, 1873. — MacGillivray, 1891. 



Isotoma capitola MacGillivray, 1896. 



Isotoma glauca MacGillivray, 1896. 



Colour very variable: dark green, greenish yellow, dull yellow, lilac, 

 blackish blue, reddish purple, leaden purple or dark brown; usually with small 

 pale dorsal spots. Without longitudinal lines, in the typical form. Eyes 

 8 + 8, subequal (fig. 48). Postantennal organs (fig. 48) broadly elliptical, oval, 

 or circular; shorter, to a little longer, than the diameter of an eye. Antennae 

 one and one-half to two times as long as the head, with segments in relative 

 lengths about as 4:7:7:8. Sense organ of third antennal segment consisting of 

 a pair of slender rods. Abdominal segments without ankylosis. Fourth 

 abdominal segment slightly shorter than the third. Ungues (fig. 49) long, 

 slender, slightly curving, with a pair of large, lateral teeth, with inner margin 

 bidentate, and with parallel basal folds. Unguiculus extending two-fifths to 

 two-thirds as far as unguis, lanceolate, unidentate near the middle of the inner 

 margin. Tenent hairs absent. Furcula strongly developed, appended appar- 

 ently to the fifth abdominal segment. Dentes slender, gradually tapering, 

 more than twice as long as manubrium, crenulate dorsally, with a distal bristle 

 extending beyond the mucro. Mucrones (fig. 50) falcately and subequftUy 

 tridentate; second and third teeth opposite , each other. Rami of tenaculum 

 quadridentate (fig. 51); corpus with numerous ventral setse. Clothing (fig. 52) 

 of dense simple or feebly serrate setse; with long outstanding fringed sensory 

 setae. Maximum length, 6 mm. (typical form); 7 mm. (var. arctica). 



The specimens of this well-known species collected by the Expedition 

 agree with my examples from Europe and the United States, but are under the 

 maximum size, being not more than 3 mm. in length. In colour they are clear 

 green with pale spots, or dark blue. 



Having examined Packard's types in the Museum of Comparative Zoology, 

 Cambridge, Mass., I agree with MacGillivray ('96, p. 58) that Isotoma Belfragei, 

 purpurascens, plumbea, and the Massachusetts specimens of tricolor, all belong 

 to viridis Bourlet. The Texas specimens, for which MacGillivray retained the 

 name of tricolor, are palustris Mtiller. 



Isotoma capitola MacG. is synonymous with viridis Bourl., as I have found 

 from a cotype sent to me by MacGillivray. 



The form referred by MacGillivray to glauca Packard is also viridis Bourl., 

 and is specifically distinct from Packard's glauca. 



Isotoma viridis is one of the most abundant collembolans, is the largest 

 known species of its genus in North America and Europe, and may easily be 

 recognized with the naked eye. It belongs primarily to the fauna of the humus, 

 and occurs in almost any soil that is not too dry — in grass lands, woods, swamps, 

 or cultivated fields — congregating under stones, pieces of wood, dead leaves or 

 other protection, and in piles of garbage or manure. It occurs in moss, on 

 pools of water, on the seashore under driftwood or seaweed, and in winter on 

 the snow. 



The typical form of Isotoma viridis, ranging throughout Europe and the 



United States, including Alaska, has been reported from the following Arctic 



localities: Siberia, Spitzbergen, Bear island, Jan Mayen, Iceland and Greenland. 



One specimen under old drift-wood logs in tundra behind house at Collinson 



Point, Alaska, Sept 27, 1913. F. Johansen. 



Two specimens, under driftwood, Demarcation point, Alaska, May 16, 

 1914. F. Johansen. 



A few specimens, under loose stones, Bernard harbour. Northwest Terri- 

 tories, May, 1915. F. Johansen. 



