Antennae cylindrical, thickest near the middle, the terminal half subulate; articulations numerous, very short, hardly perceptible. Palpi thick, scaly; frontal side obtuse; lateral sides compressed; the margins externally fringed with hair; the last joint naked, lengthened, nearly horizontal, linear, compressed. Eyes (in the male) very large. Body (in the male) of seven joints, the last with a transverse, slightly emarginate, truncate appendage above; and two obtuse recurved hooks below, concealed by a tuft of hair; the first and last segment shortest. Body in the female with the last joint lengthened and pointed. * * * * * SPECIFIC CHARACTER. _I. alis supra fuscis, basi nitide-caerulea, posticis aurantio marginatis, subtus rufo-fusco nebulosis, basi puncto nigro: anticis (in maribus) basi aurantiis, macula nigra tomentosa._ Wings above fuscous, shining blue at their base; posterior margined with orange; beneath clouded with rufous and brown, and a black dot at the base of the posterior wings. Anterior wings (in the male) orange at the base, and a large velvet-like spot of black. * * * * * The resplendent and changeable azure blue which ornaments the body and part of the wings in this very singular insect, can be but ill expressed in the figure. It is one of the many new and interesting subjects in entomology discovered in Java by Dr. Horsfield; and by his kindness and liberality I am enabled to add the figures of the caterpillar and chrysalis, which were copied out of a fine series of drawings made in Java under his own eye: they do not appear to differ in their formation from others of this family, although the perfect insect possesses such striking and peculiar generic characters; one of the many facts which prove the impossibility of making the _Larvae_ a primary consideration in forming the genera of Lepidoptera. This is a rare insect, I have therefore been obliged to leave the generic character imperfect, as the dissection of the mouth, &c. would destroy the specimen. The posterior margin in the wings of the male is sinuated; in the female it is nearly straight; the underside of the wings in both sexes is the same; the anterior pair reddish-brown, paler in the middle; the tip and posterior margin whitish: inferior wings reddish-orange towards the inner margin, with an obsolete central curved band of the same, and a black dot at the base of the inferior wings. The head, palpi, and thorax are margined with orange, less conspicuous in the female. Our knowledge of the genus _Hesperia_ of Latreille (under which the present insect would come) is little more than what was known of _Scarabaeus_ twenty years ago; nor has Fabricius even noticed one half of the species figured by Cramer. The larva feeds on GAERTNERA _Javensis_