B. hamiltoni n. sp.

Eyes holoptic on front in both sexes, covering sides and top of head. Antennae inserted about middle line of head, prominent, densely pubescent, blackish-brown, a golden pubescence particularly noticeable on style, which is two-jointed, basal joint short, terminal joint ending in short naked spine-like process, the two joints together being about as long as clavate third antennal joint (fig. 38). Face bare, short, shorter than broad, greyish-white but blackish along orbits. Cheeks bare, cuneiform, concave, blackish with greyish reflection. Occiput flat, somewhat depressed above foramen but rather swollen beneath and slightly descending at posterior oral margin; black in ground-colour but with distinct greyish-yellow tomentum, sparsely clothed with delicate yellowish-brown hairs below and row of delicate short black orbital bristles above foramen. Ocellar triangle prominent, blackish-brown, ocelli golden; pair of prominent ocellar bristles. Proboscis and palpi withdrawn, blackish-brown with somewhat lighter reflections; apex of proboscis shiny black; palpi bristly.

Thorax distinctly humped in profile; prothorax and humeri greyish-yellow, the former dusky on each side in certain lights; dorsum velvet-brown, a greyish-yellow stripe on each side, with reddish tinge, extending from humeri to alar angles, outside of which is a velvet-brown narrow stripe from humeri to wing-bases; alar angles greyish-yellow; a broad light-brown medio-longitudinal stripe (indistinct in some lights except at scutellum) extending from near prothorax and broadening toward scutellum, which is greyish-yellow; in certain lights the darker colours of dorsum merge in front of scutellum into the lighter; metathorax greyish-brown. Dorsum bare except for a few small bristles (fig. 39), the series toward root of wing, however, being large and conspicuous; a fringe of delicate, rather reclinate bristles along anterior margin of prothorax; scutellum with fringe of delicate bristle-like hairs.

Wings (fig. 40) clouded with brown, more so apically, a clear space on each side of stigma which is opaque-brown; veins brown; anal angle prominent; R₄ not strongly recurved; no supernumerary cross-vein between R₂₊₃ and R₄₊₅; apex of cell Cu somewhat obtuse in comparison with that of B. adelensis. Halteres light-yellow.

Legs black with silvery rather yellowish-grey reflection, which is particularly persistent on coxae. Middle legs shorter than others and with swollen femora; anterior and posterior legs slender but apex of tibiae and protarsi slightly thickened. Leg chaetotaxy as in B. adelensis.

Abdomen blackish-brown, with delicate pale hairs at sides; basal and second segments greyish-brown, and a greyish-brown triangular area toward posterior angles of each segment, upon which is a paler brown and indistinct band; this pattern seen only in certain lights. Male genitalia (fig. 41) black, claspers bristly and each terminating in stout bristles; their inner edges not spined; median ventral process bare and shiny; whole genitalia directed upwards. A pair of spots on sides of each abdominal segment except first; on second segment a double row on each side along posterior margin.

♂. Length, 8 mm. ♀. Length, 8·5 mm.

Syntypes: No. 1226, D. M.

Habitat.—Te Wairoa. A very common species in vicinity of waterfall.