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.
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.
(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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