In the second and smaller group of the Pharmacophagus Swallow-tails the general colour scheme is a more or less dark metallic blue-green with a tendency towards the obliteration of light markings. Some idea of their appearance may be got from the figure of the Central and N. American _P. philenor_ on Pl. XVI, fig. 1. Though one or two unprotected Papilios in S. America fall more or less into this colour scheme, the group, from the point of view of mimicry, is not nearly so important as the red-spotted one. Nevertheless the blue-green Pharmacophagus group as represented by _P. philenor_ is supposed to play a considerable part in mimicry in N. America. _P. philenor_ is found throughout the greater part of the Eastern United States, straggling up as far as the Canadian border. On the west it is also found reaching up to North California. Over considerable parts of its range are three other Swallow-tails, belonging to the unprotected Papilios, which are regarded by Professor Poulton and others as mimics of _philenor_[22]. One of these, _P. troilus_, is dark brown with a dusting of blue scales over the hind wing (Pl. XVI, fig. 2). The sexes here are more or less alike. _Troilus_ stretches up into North-west Canada some way beyond the limits reached by its model. _P. glaucus_ is a black and yellow Swallow-tail with two forms of female. {46} One of these resembles the male while the other is darker and is said to mimic _philenor_. It is known as the _turnus_ form and is found more commonly in the southern part of the range of the species, _i.e._ in the country where _philenor_ is more plentiful. The third species, _P. asterius_, has a more southerly distribution. Its female is darker and nearer to _philenor_ than the male. It must, however, be admitted that none of the three species bears a very close resemblance to _philenor_. It is suggested that this is because _P. philenor_ is a tropical form which has only recently invaded N. America. The crossing of _philenor_ has, as it were, induced the three mimicking _Papilios_ to turn dark, but the model has not been long enough in contact with them for the likeness to become a close one. The explanation, however, hardly accounts for the fact that the best mimic of the three, _P. troilus_, in which both sexes are dark, is found far north of _philenor_. Either the dark colour was established without the influence of the Pharmacophagus model, or else the species rapidly extended its range northwards after having been modified under the influence of _philenor_ in the south. But in that case the critic may ask why it does not revert to the original pattern now that it has got beyond the model's sphere of influence. On the whole it seems at present quite doubtful whether any relation of a mimetic nature exists between _P. philenor_ and these three species of _Papilio_.