In a recent examination of the rich collection of fossil insects from Aix, preserved in the Museum of the city of Marseilles, my attention was attracted by two little slabs containing the traces of a fossil butterfly. Although by no means so well preserved, nor so perfect as the remains of a butterfly from the same beds, described by Dr. Boisduval more than thirty years ago, a glance showed that it could not be referred to that species, since the costal nervure of the fore wings was greatly swollen. No such form having to my knowledge been described from these beds, Dr. Reynès, the accomplished director of the establishment, courteously placed the best specimen in my hands for closer study; and from it the following account and illustrations have been drawn. The second specimen is very imperfectly preserved, but since it exhibits in all its features an exact resemblance to similar parts in the better specimen it undoubtedly belongs to the same species. The fossil (Pl. I, fig. 2) is a natural cast of a butterfly lying upon its side, the wings folded back to back, the legs extended as if hanging, the tongue uncurled and, with the antennæ, drooping in a direction similar to that of the legs. The right fore wing, which lies beneath, is pushed a little outward and also forward, even at its base, showing that the specimen must have been greatly macerated in very quiet water, before being covered by the deposits which have preserved its more essential features. The condition and position of all the parts also lead us to conjecture that it was swept into its final resting place by a gentle current, which left the slighter appendages lying in the direction of its final action. It is evident that the object is a cast, for the veins of the wing which lie uppermost on the stone are impressed as we see them on the upper surface of the wings of living Oreades, while those of the wing lying beneath (veins which are plainly covered by the impressed nervures where the two come in contact) are in relief, as seen on the under surface of the same butterflies; that is, we have here the reverse of what would be the case, were we examining a living butterfly in this position.