This very widespread genus is remarkable for the peculiar formation of the branches of the media in both wings. In the forewing, M₂ and M₃ are fused together for some distance basally, thus forming an apparent apical fork between them when they diverge distally, much in the same way as has been described above for males of the genus Neurochorema. In the hindwing, where M₄ is absent, this same fusion takes place between M₂ and M₃₊₄ basally, and results in the apparent presence of three veins, M₁₊₂, M₃, and M₄, though these are actually M₁, M₂, and M₃₊₄ respectively. This transference of vein M₂ on to a common stalk with M₃₊₄ in this wing led Ulmer to state that Af₄ was present in the hindwing of this genus and of the allied Australian genus Saetotricha. As a matter of fact, Af₄ is never present in the hindwing of any Trichopteron, since M₄ naver exists as a separate vein.

The larval characteristics of the genus are well known, the generic name having been given from the helicoid form of the case, which is composed of grains of sand, and is so beautifully modelled as to appear almost exactly like a small snail-shell. To accommodate itself to its peculiar home the larva has become greatly elongated.

Genotype.—Helicopsyche borealis Hagen. (North America.)

Only a single species has so far been recorded from New Zealand—viz., H. zelandica Hudson (Plate 19, fig. 18)—more fully described by Hare in 1910, Hudson's original description being very scanty. Two more species are here added, making three for the Dominion. They may be distinguished by the following key:—

Helicopsyche albescens n. sp. (Plate 19, fig. 19; text-fig. 26.)

♂. Total length, 3mm.; forewing, 4.5 mm.; expanse, 9.5 mm.

The whole of the head, thorax, and abdomen dull brownish-testaceous, except eyes, which are blackish, and antennae, which are testaceous; legs pale greyish-testaceous.

Wings semitransparent whitish, with very pale greyish hairs and fringe; venation pale-greyish. Appendages of very characteristic form, as may be seen from text-fig. 26; process of tenth tergite wider at base than at apex, and the latter triangularly incised and carries four short stiff bristles; pre-anals short and slender; gonapophyses very large, two-branched, and exceedingly hairy.

Types.—Holotype male, allotype female, and series of paratype males, Purau Creek, Lyttelton Harbour (3rd January, 1920, R. J. T.); all in Cawthron Institute collection.