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120 CALLIDRYAS.

genus is composed of a selection of species from Colias, to which it bears a very close relation. It is not long since it was proposed by Dr Boisduval, who thinks that the following characters entitle it to this distinction. Palpi approximating and very much compressed, clothed with short hairs and dense scales, the terminal joint conical and much shorter than the preceding one; antennæ thickening gradually from the base to the apex, which is distinctly truncated; body robust, the abdomen much shorter than the inferior wings; the latter forming a groove which completely embraces the under side of the abdomen. The caterpillars are naked and somewhat attenuated at both extremities; the chrysalis arched, or boat shaped, with the extremities drawn out to a narrow point; always attached by the tail and a transverse band.

According to the manner in which they have been respectively constituted, Callidryas therefore is best distinguished from Colias by the antennæ, which in the latter terminate in an obconical club; and from Rhodocera (including Gonopteryx of Dr. Leach), which has these organs likewise truncated, by the shape of the wings, which never present acute angular projections. The prevailing colour of the