The present generic group was first separated from _Papilio_ by Dr. Boisduval. None of its characters, taken singly, are very strongly marked, but their aggregate importance is sufficiently considerable to authorise its adoption. As in _Papilio_ the antennæ form an elongate club, having the extremity slightly curved upwards, the palpi are longer than in the genus just named, but they never rise above the forehead. The prothorax is much developed anteriorly, and forms a pretty distinct neck. The abdomen is long and robust, that of the male deeply grooved on the under side, and provided at the anal extremity with two large rounded valves. The wings are large, of a strong texture, and furnished with salient nervures; the anterior pair elongate; the posterior with wide shallow indentations, and never prolonged into a tail. We are very imperfectly acquainted with the natural history of the insects of this group in their early stages. Their remote localities, and the rarity of most of the species, have, for the most part, prevented them from falling under the notice of competent observers. The caterpillar and metamorphoses of one of them (_O. Heliacon_), however, have been described by Dr. Horsfield. Like the caterpillars of _Papilio_, it is furnished with two retractile tentacula; the body is large and thick, and bears eight rows of rather long fleshy prominences, of a conical shape. The chrysalis into which it is transformed is somewhat curved, having the head obtuse, and a few projecting points above the middle. It is suspended by the tail, and a transverse band, which, however, does not encompass the body, but is inserted on each side. (See Fig.) [Illustration] This group is but of limited extent, but it comprehends some of the largest and most beautiful lepidoptera yet known to us. With one exception, which extends over a portion of the Indian continent, they are confined to the Mollucca, Philippine, and others of the numerous and extensive islands of the Indian Archipelago. The species figured, which is the most beautiful of the whole, and to which Linnæus applies the epithet of _august_, has been long known and highly prized by collectors. It is named [Illustration: PLATE 1. _1 Ornithoptera Priamus_ _2 Ornithoptera Remus_ Natives of the island of Amboina.] ORNITHOPTERA PRIAMUS. PLATE 1. Fig. 1. _Boisd. Species gener. des Lepidop._, 173.--Papilio Priamus, _Linn. Latr. Godart, Cramer_; _Papillons exotiques_, 23, A, B; _Donovan’s Insects of India_, Pl. 3. Female, Pap. Panthous, _Linn._; _Cramer_, 123, A, and 124, A; _Don. Ins. of India_, Pl. 2.