This tiny species is found commonly amongst the roots of the herbage in very moist places. It presents a horny translucent appearance and is of a reddish brown colour. It runs with considerable speed, and when it is moving, the white irregular lines with which it is beset are not evident. Trichoniscus pusillus is very much like Trichoniscus vividus in colour but the latter species is nearly twice as big and has from five to seven joints to the flagellum, while the former has never more than four. Trichoniscus roseus is also much larger and its bright red colour (which it loses, however, when preserved in alcohol) is another means of distinguishing it from the species under consideration.
Professor Sars in his Crustacea of Norway (p. 162) describes from Christiania, under the name of Trichoniscus pygmæus, a still smaller species. As this may possibly be discovered in this country a brief comparison between it and Trichoniscus pusillus may be of value. The former reaches a length of but two millimetres; it is "whitish, semi-pellucid with a few light brown pigmentary ramifications across the segments and a double row of irregular opaque patches along the middle of its back" (p. 163). Its body is covered with minute tubercles and there are only three joints to the flagellum; its movements are by no means rapid.
The body of Trichoniscus pusillus is smooth and polished. It has four joints to the flagellum—Dr. Scharff (63) says three or four—and it moves quickly.
BRITISH LOCALITIES:—
England: Brightlingsea; Warley; (W.M.W.): Epping Forest; (Bate and Westwood, 1): Hanwell; Southall; Kew Gardens; Langley; Burnham Beeches; Dropmore; Skirmett; Bluebell Hill, Maidstone; (W.M.W.): Chislehurst; Plymouth; Polperro; Looe; (Bate and Westwood, 1): Hertfordshire; Northumberland; Durham; (Norman, 49): Exeter; (Parfitt, 53).
Scotland: Edinburgh; (Scott, 68): Cumbrae; (Robertson, 57).
Ireland: Connemara; (Norman, 49): Dublin; Wexford; Cork and Kerry; (Percival Wright teste Bate and Westwood, 1): Tyrone; Waterford; Portlaw; Kilkenny; Wicklow; (Kinahan, 33).
FOREIGN DISTRIBUTION:—