10 A Canadian Arctic Expedition, 1913-18 
Isotoma palustris Tullberg, 1871, 1872, 1876.— Uzel, 1890. 
Isotoma Belfragei Packard, 1873. — MacGillivray, 1891. 
Isotoma tricolor Packard, 1873 (part). — -MacGillivray, 1891 (part). 
Isotoma purpurascens Packard, 1873. — MacGillivray, 1891. 
Isotoma plumbea Packard, 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 subequally 
tridentate; second and third teeth opposite each other. Rami of tenaculum 
quadridentate (fig. 51); corpus with numerous ventral setae. Clothing (fig, 52) 
of dense simple or feebly serrate setae; 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 MacGilhvray retained the 
name of tricolor, are palustris Miiller. 
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, w^oods, 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 beeo ropoi'ted from the following Arctic 
locahtics: Siberia, Spitzl)ergen, Bear island, Jan Mayen, Iceland and Greenland. 
One specimen under old drift-wood logs in tundra behind house at CoUinson 
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. 
