Of this distinct and very remarkable genus of Volutes, few species have hitherto been discovered: the subordinate divisions cannot therefore be traced; nor do we feel satisfied that all the typical characters have been detected: we consider it nevertheless, as a perfectly natural genus, absolutely essential to mark the connection between the Volutes and the _Marginillæ_. Lamark, indeed, as if aware of this affinity, actually describes one species as a _Marginilla_. The union of the three aberrant genera of _Scaphella_, _Volutilithes_, and _Harpula_, into one circle, is effected by the _Scap. papillaris_ and the _Harpula Lapponica_: the former species conducting us at the same time to the typical Volutes, by means of _Voluta fulgetrum_ of Sowerby. _Scaphella maculata_ is a native of the Australian seas, and is of great rarity. Our drawings were made from one of the beautiful specimens in Mr. Broderip's possession, It is probable that the animals of this genus envelope their shells in an ample mantle, since they are almost always enamelled. * * * * * * [Illustration: ARCAS _Imperialis_.] ARCAS imperialis. _Emerald Hair-streak._ ---- Tribe, Papiliones. Family, Polyommatidæ. Sub-family, Theclanæ, _Nob._ SUB-GENERIC CHARACTER. Palpi, in both sexes, very long, thick, porrect, twice as long as the head, curved downwards, all the joints entirely covered with close-set scales, posterior wings six-tailed. ---- SPECIFIC CHARACTER. _Above shining blue: beneath emerald-green, marked with minute black waved lines._ Papilio imperialis. _Cramer, Pl. 75. f. E. F._ Hesperia Venus. _Fab. Ent. Sys. 3. 1. 268._ ---- It is impossible to depicture with correctness, the resplendant blue which ornaments the upper surface, or the vivid emerald green on the under wings, of this rare and splendid insect. It is possessed by few collectors; nor did we capture more than three specimens, during two years devoted to the entomology and ornithology of Brazil. The male is distinguished by a black central spot on the anterior wings. The very remarkable prolongation of the palpi, which are alike in both sexes, induces us to consider this insect as a type of form, or in other words, a sub-genus: but we are at present unprepared to state any thing satisfactory on its true affinities. We have thought it right in this and other instances, to retain the original specific name of Cramer; and we shall do the same in all instances where it will not produce a discordant union of generic and specific names. On this head, as the principle of Linnæus, from the great number of new genera since defined, can no longer be acted upon, we think that specific appellations, derived from some character of the insect, are much better, in every respect, than attempting to render the nomenclature of the Lepidoptera a correct index to the mythology of the Ancients. * * * * * *