Length (excluding setae)—Male, 6.5 mm.; female, 4.5 mm.
Head—Burnt umber. Eyes of female, dark olive; those of male, dark olive in lower lobes, bright orange red, very large and conspicuous in upper ones. Ocelli, light grey.
Abdomen—Male: posterior four segments brown ochre, except anterior of seventh segment, which is whitish: anterior segments whitish with posterior and lateral edges dark brown. Female: burnt umber, first eight segments dark rimmed posteriorly. Claspers three-segmented, light brown basally, becoming light fawn or flavescent distally.
Penes light fawn.
Caudal setae white, with black joinings.
Legs—Femora luteous with dark mark distally. Tibiae somewhat lighter, also with dark mark distally. Tarsi fawn, dark-marked at joinings. Claws dissimilar.
Wings hyaline and very iridescent. Veins light brown, inconspicuous, C., Sc. and R1 more strongly marked than the others. Cross-veins colourless: hm. not coloured (as it is in D. cromwelli, a rather similar fly in other respects, which appears at the same season). Bullae on Sc., R1 and R2a.
Wing length, 6.5 to 7 mm.
The costa, except towards the ends, is less strongly marked than Sc. and R1, giving the wing a particularly fragile appearance.
Egg—Regularly oval; clouded milky; chorion covered with rounded bosses. Egg-mass yellow.
Wings—Waxen-coloured: wing-base showing up markedly white. Cross-veins almost invisible. This stage lasts about 24 hours.
The nymph has not been identified for certain, but from the appearance of exuviae, it would seem to be a typical small Deleatidium nymph, 5.5 mm. long, with the posterior segments of the abdomen lighter than the anterior-ones, small wing-pads, dilated femora, outer caudal seta 6 mm. long, median one 7.5. The gills are single, relatively narrower than in D. lillii and more ovate and acuminate in shape.
Distribution—R. Hutt, Wellington district.