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Show 482 PROF. J. O. WESTWOOD ON INDIAN BUTTERFLIES. [Apr. 5, which agrees with Mr. G. R. Gray's " variety a " above mentioned ; and figure 4 represents the underside of the hind wing of the typical P. pollux. Plate X L V . fig. 2 represents a female insect from " India" in the Hopeian Collection, measuring 4f inches in the expanse of the fore wings, which agrees with the female P. pollux, except that the discoidal fascia of the hind wings is reduced to a row of large hastate marks beyond the middle of the wing, not reaching upwards to the discoidal cell, more than half the basal portion of the wing thus being of uniform rich brown colour, slightly suffused beyond the middle with fulvous scales-the fascia of hastate spots being but slightly irrorated with dark scales, especially on the underside, and extending across the wing to the anal margin. The hind wings of this female specimen are of the rounded form of the ordinary females of P. pollux. I have now to direct attention to another specimen from " India," also in the Hopeian collection, figured in Plate X L V . fig. 1, which is unquestionably a male, although it agrees so entirely in shape, colour, and markings with the female represented in fig. 2 on the same plate that it would be difficult to distinguish between them. Here, therefore, we have a clear proof that the opposite sexes of the same species do not differ from each other, except in internal sexual organization. Mr. Wood-Mason (Journal of the Asiatic Society of Bengal, vol. xlix. part ii. 1880, p. 144, plates viii. and ix.) has lately described the two last above-mentioned insects as the sexes of a new species, and has applied to it the name P. dravidarum, of which he has given a figure of the upperside alone of the male. The specimens described by Mr. Wood-Mason were received from the Kadur district, Mysore, and from Trevandrum. He considers m y P. castor and P. pollux as the two sexes of a distinct species, observing that in P . castor " the sexes are, as regards colour and markings, as strongly differentiated from one another as in any species with which I am acquainted ; they also differ to some extent in form, the male having the fore wing narrower, with the external margin obviously emarginate, and the hind wing also narrower and produced, with the same margin more deeply incised and lobed than in the female, both pairs of whose wings in form more or less closely resemble those of both sexes in the other two species," P. dravidarum and P. mahadesa from Bur-mah, whilst "in P. dravidarum the sexes agree perfectly both in form of the wings and markings, differing very slightly in colour only; so that but little sexual differentiation has here taken place." With respect to the females of m y P. pollux, M r . Wood-Mason states that specimens from Assam, Cherra Punji, and Silhet have rounded hind wings, |whilst others from Silhet and Sikkim have " the third branch of the median vein produced into a small tooth." Of one of these he gives a figure, named P. castor $ , describing these latter specimens as having more distinctly cream-coloured hind wings than the rounded-winged ones. One of these light-coloured- |