The Butterflys composing this remarkable genus are perhaps the most splendid insects in creation. No art can effectually represent the changeable and resplendent green which relieves the velvet black of the wings, and which varies with every change of light. The typical species are found in Tropical America, where they fly with amazing rapidity, and perform, like their prototypes the Swallows, annual migrations. When at rest, the anterior wings are flat or horizontal, but only slightly spread. The present species appears confined to Surinam. Modern systematists have been peculiarly unfortunate in the location and construction of this group; while the name of _Urania_, bestowed upon it by Fabricius, has long been appropriated to a genus of plants. Linnæus, more correctly, placed it with the genuine _Papiliones_; a station which is confirmed by the details of its structure: the anterior feet, like those of _Leptocircus_, figured at pl. 106, being provided with that short spiney process, which is a peculiar distinction of this sub-family. The analogies which result from this location of _Leilus_ are beautiful, and almost interminable. It is the representation of the _Noctuidæ_ and of the _Hesperidæ_ in its own circle; and of the fissirostral tribe of birds; all these being modifications of the natatorial type of the VERTEBRATA. * * * * * * [Illustration: LEILUS _Brasiliensis_. _Sw._] LEILUS Braziliensis. _Brazilian Emerald Butterfly._ ---- SUB-GENERIC CHARACTER. _Wings_ when at rest, horizontal, slightly expanded; posterior furnished with acute tails. Palpi short, porrect; the last joint nearly naked, projecting beyond the head, but shorter than the second joint. _Tibiæ_ of the anterior feet, spined in the middle: claws very small. _Antennæ_ filiform, thickened in the middle; the tips bending outwards, but not uncinate. _Sw._ ---- SPECIFIC CHARACTER. _Wings black, varied with lines and bands of golden green: posterior wings tailed, the green spots round the margin divided and insulated; the tails black, with a narrow white edge._ In Mus. Britt. Nost. ---- This species, hitherto confounded with that peculiar to Surinam, is found only in Brazil; but its precise geographic range, in that vast empire, has not been correctly ascertained. We had the pleasure of capturing several specimens in Lat. 8, 24, S. in the vicinity of Pernambuco, where great numbers appear during the early weeks of May, and again in June.