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Mustilia Walker

Types species: falcipennis Walker.

The venation of this and the following genera has been described in the introductions to the family and is illustrated for the only Bornean species in Fig. 4.

Figure 4. Venation in the two lineages of the Bombycidae: left, Mustilia dierli; right, Ocinara albiceps.

The forewings are strongly falcate with no angle at the centre of the margin. Sexual dimorphism is slight. The forewing has an oblique postmedial that angles back to the costa at one quarter from it, though it appears to continue to the apex smoothly through a shade from the apex to the angle. The antemedial is more irregular; there is usually a dark discal spot between the fasciae. The wing distal to the postmedial is usually at least partly darker than the area basad. The coloration is usually rich brown or greyish brown.

In the male genitalia the uncus is bifid or bilobed. The gnathus is divided in the type species as in Andraca Walker, but lost in the species described below. The valve is simple, elongate, with a diagnostic setose furca at the base of the sacculus. The saccus is weak. The aedeagus vesica is evenly scobinate in the type species but with groups and bands of heavy spines in the species discussed below. The eighth tergite is bilobed or with a central notch.

The female genitalia (falcipennis) have the eighth segment deep, the ductus bursae short, broad, slightly twisted and sclerotised centrally, and the bursa with a horse-shoe-shaped scobinate signum.

Sevastopulo (1946) described the fully grown larva of the type species. The body is dark brown, speckled with minute yellow dots within each of which there is a short bristle. The first five segments are darker than the rest; beyond them there is a dark dorsal stripe of varying width, and a narrow black dorsal line on the thorax itself. There is an extensile sublateral flap of skin on the metathoracic and two anterior abdominal segments; below this on the forepart of the metathorax is a small, black-ringed, orange, inflatable organ. There is a long, fleshy, downturned horn on A8. On disturbance the flap is expanded, with the head and anterior part of the thorax retracted, the inflatable organ expands to resemble an eye, and the caudal horn is lashed from side to side.

Pupation is in a small cocoon of tough brown silk spun amongst leaves.

Apart from the species described below there are two other species in the genus recorded from Sundaland: lieftincki Roepke from the mountains of Sumatra and the Taiwanese gerontica West, or a very similar species, in the mountains of Peninsular Malaysia

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