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Seen by transmitted light the wing-cover is of a very pale reddish colour, excepting two large adjacent spaces, one of which, the larger and anterior, is triangular in shape, while the other, the smaller and posterior, is oval. Each space is surrounded by a strong nervure and goffered by slight wrinkles or depressions.
This segment is bent at a right angle along a strong longitudinal nervure, and descends on the outer side in a flap which encloses the insect's flank when in the attitude of repose. The right wing-cover overlaps the left.
In our British Phasgonura viridissima it appeared to me that the serrated nervure is rubbed against the rounded hind-corner of the opposite wing, the edge of which is thickened, coloured brown, and very sharp. In the right wing, but not in the left, there is a little plate, as transparent as talc, surrounded by nervures, and called the speculum.
Anterior wings fuscous, with a pale vitta commencing near the base on the subcostal nervure, reaching the costa before the middle, and extending along it to the apex, where it joins a flexuous submarginal band, connected with a vitta occupying the whole inner margin; beyond the cell is an abbreviated flexuous striga; followed by a subquadrate dot; posterior wings pale dull red, with a broad submarginal fuscous band, and a discoidal spot of the same colour; head and anterior part of thorax pale, posterior black; abdomen above red, with a black dorsal line; antennae fuscous; femora red; tibiae and tarsi fuscous.
He says, "It is remarkable for having a sort of drum at the base of the fore wings, between the costal nervure and the subcostal. These two nervures, moreover, have a peculiar screw-like diaphragm or vessel in the interior." The noise was continued at short intervals, and could be distinguished at about twenty yards' distance: I am certain there is no error in the observation.
This last nervure, which is of a slightly reddish hue, is the fundamental element of the musical device; it is, in short, the bow, the fiddlestick, as is proved by the fine notches which run across it. The rest of the wing-cover shows a few more nervures of less importance, which hold the membrane stretched tight, but do not form part of the friction apparatus.
He says, "It is remarkable for having a sort of drum at the base of the fore wings, between the costal nervure and the subcostal. These two nervures, moreover, have a peculiar screw-like diaphragm or vessel in the interior." Catherine's on the coast of Brazil, a butterfly called Februa Hoffmanseggi, makes a noise, when flying away, like a rattle.
The projecting portions of both wing-cases are traversed by a similar strong nervure, but this is scored like a file only in one of them, in the other remaining perfectly smooth.
On one wing this horny expansion is furnished with a sharp raised margin; on the other, the strong nervure which traverses it on the other side is crossed by a number of short, sharp furrows, like those of a file. When, therefore, the insect rapidly moves its wings, the file of one expansion scrapes sharply across the horny margin of the other, thus producing the curious sounds.
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