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Ameletus flavitinctus n. sp.
♀. Imago: Total length, 18 mm.; forewing, 19·5 mm.; hindwing, 7 mm.; expanse, 41 mm.
Head (somewhat shrivelled) small, dull medium brown; eyes dull-blackish.
Thorax: Pro- and meso-thorax rich umber-brown above; metathorax dark chocolate-brown above; sides dull brown shading to pale brown beneath; mesonotum with two blackish marks placed close up on either side of the median suture posteriorly. Legs short, pale brown, the femora with a broad black median band and a narrower black band at apex; tibiae marked with black apically; tarsi blackish, except for the bases of the first three segments, which are pale-brownish. Fig. 2, g, shows the tarsus of the hind leg, for comparison with that of Ameletus ornatus (fig. 2, h), an insect of somewhat smaller size but with much larger legs.
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Abdomen narrow subcylindrical, tapering posteriorly. Segments 1–6 dark brown, heavily marked with dull-blackish in the form of a transverse basal band, from which project two elongated longitudinal marks, one on either side of the median line, and reaching to within a short distance of the apex of each segment; 7–8 paler brown, with similar blackish basal band, but with shorter longitudinal projecting marks, reaching only about half-way along each segment; 9 pale brown, with very narrow blackish basal band and slender longitudinal projecting marks; 10 pale brown, with narrow blackish basal band and no projecting marks. Ventral valve cleft in middle, its margin forming two rounded lobes (fig. 2, f); those of the other New Zealand species are shown for comparison in fig. 2, d, e. Cerci (partially shrivelled) somewhat longer than abdomen, brown, with darker segmental rings. Appendix dorsalis much reduced, only 3 mm. long, much shrivelled, with numerous minute obsolescent segments.
Fig. 1.—Ameletus fiavitinctus n. sp.: female imago, wings. × 5·4. The shaded portions of the wing represent the parts coloured pale transparent yellow, the unshaded portions those which are hyaline. Cu, cubitus; M, media; R, radius; So, subcosta. Note the positions of the two groups of thickened cross-veins and of the bullae in the forewing.
Wings brilliant, most of the membrane a pale transparent yellowish, but with certain areas left absolutely hyaline, as shown in fig. 1. It will be seen that these areas are chiefly those formed where the very irregularly placed cross-veins lie farthest apart. Veins blackish. Forewing with two groups of thickened black cross-veins between Sc, R1, and R2, one set being about half-way along the wing, the other below the proximal part of the pterostigma. There is a series of five definite spots or bullae on the forewing, on Sc, R1, R2, R3, and R4 respectively, the first three being large and situated in the midst of the first set of thickened cross-veins already mentioned, while the last two are smaller and situated below them. In shape the forewing is similar to that of Ameletus ornatus Eaton. Hind-wing with the humeral angle as shown in fig. 2, c; the same portion of the hindwings of A. perscitus Eaton and A. ornatus Eaton are shown for comparison in fig. 2, a, b.
♀. Subimago: The specimen described above was captured in the subimaginal stage, but had changed into the imaginal stage before it was killed. The subimaginal stage has opaque wings, remarkably variegated in the bold manner shown in the subimago of Atalophlebia versicolor Eaton.
Male unknown.
Type.—Holotype female imago in Cawthron Institute collection.
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Locality.—Stream above high waterfall at Wahi, near Tokaanu, southern end of Lake Taupo, 26th November, 1919 (R. J. T.).
This fine species is easily distinguished from A. perscitus by its slenderer build, its narrower wings with much less dense venation, and by the yellow colouring of the wings being paler and not covering the whole wing. It is more closely allied to A. ornatus, which it resembles closely in shape and venation, but can be at once distinguished from it by the colour-pattern of the wings both in the imago and subimago, by the presence of the two groups of thickened cross-veins on the forewing (A. ornatus ♀ has only the single group around the bullae), by the shape of the humeral angle of the hindwing, by the shortness and slenderness of the legs, and finally by the very differently shaped ventral valve. It should
Fig. 2.—Details of the morphology of the female imago in the three New Zealand species of Ameletus: a, A. perscitus Eaton, humeral angle of hindwing; b, the same in A. ornatus Eaton; c, the same in A. flavitinctus n. sp.; d, A. perscitus Eaton, ventral valve; e, the same in A. ornatus Eaton; f, the same in A. flavitinctus n. sp.; g, A. flavitinctus n. sp., hind tarsus; h, A. ornatus Eaton, hind tarsus. All figures × 14.
be noted, however, that some fémale imagines of A. ornatus show slight yellow colouring along the costal margin of the forewing, this tint being distinctly more greenish-yellow than lemon-yellow, and giving the insećt a very peculiar appearance.
It seems advisable here to point out that A. perscitus Eaton differs very greatly from both A. ornatus Eaton and A. flavitinctus n. sp. in the shape of its wings, the density and regularity of their cross-venation, and in the remarkable structure of its large-headed larva. These characters, taken together, suggest that it is not really congeneric with them. Further than this, a study of the three New Zealand species shows that they differ considerably from the genotype, A. subnotatus Eaton, from North America, and it appears probable that they may have to be placed in two new genera.