Antennae moderate, the club lengthened, slender, cylindric. Palpi short, much compressed, obtuse, remote, not touching the tongue, covered equally on both sides with thickset hairs concealing the joints. Abdomen (in the male) 7-jointed, the first very long, the last simple, truncate, and entire above, without valves, and with an incurved hook beneath. Anterior wings (in the male) dilated at the posterior base, concealing a tuft of hair on the inferior wings. Generic Type _Papilio Jairus_. Fabr. (OBS. Wings very entire, sub-diaphanous. Hinder wings large, orbicular. Fore-legs spurious. Basal articulations of the antennae thickened at the end.) * * * * * SPECIFIC CHARACTER. _D. alis anticis angustatis, fuscis, concoloribus; margine posteriore et exteriore aequalibus: posticis albidis; margine exteriore fusco, supra uni-ocellato, subtus bi-ocellato._ Wings, anterior, narrowed, the posterior and exterior margins equal, uniform brown; posterior cream-coloured, with a brown margin, one ocellate spot above, and two beneath. * * * * * This new and elegant insect was discovered by my worthy friend Dr. Horsfield (after whom I have named it) in the interior of Java: it forms a part of the extensive collections made there by this zealous naturalist for the East India Company, and which will make a most important addition to our present confined knowledge of the productions of that interesting island: indeed these collections exceed in extent, preservation, and value, any which have been brought to this country. The general resemblance of this species with _Papilio Jairus_ of Fabricius is so great, that it might pass on a cursory view as a mere variety, did not the form of the anterior wings at once point out the difference. In the present insect the posterior and exterior margins are of equal length, giving a narrow appearance to the wings, much resembling some of the true _Papilionidae_; but in _P. Jairus_, these wings are much broader, more obtuse, and the length of the posterior margin much greater; other minor differences exist in the colouring and markings. My valued friend A. H. Haworth, Esq., F.L.S., &c. possesses a fine pair of the true _P. Jairus_ in his rich and extensive collection; and the liberality with which it is constantly and freely opened to me, deserves my warmest thanks.