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Show 1897.] MR. W. E. COLLINGE ON EUROPEAN SLUGS. 443 variety of A. empiricorum,, Fer., from Roundhay near Leeds. It was of an almost pure white, not the creamy-yellow variety which is much commoner. For some months the specimen was kept alive beneath a bell-jar on a large flower-pot, and liberally supplied with leaves of lettuce, cabbage, &c. During this period I witnessed a complete reversion to the typical black form. After I had kept the animal for about five weeks, I noticed that it looked much dirtier than previously, and about the seventh week it was a very dirty white, which quickly changed into a faint sepia. About the ninth week it became very inactive, and for three weeks, whenever I examined it, it was drawn up in the peculiar arched form so characteristic of this and a few other species of Arion. During this time a large amount of thick dark yellow slime was exuded from the caudal mucous pore, and remained over the postero-dorsal region of the body. Little by little the colour deepened, and the animal became more active about the middle of the fourth month, by which time it was almost black: by the end of the fifth month it was impossible to distinguish it from the typical black forms. I have previously seen examples of this Slug undergo slight changes in colour, such as the black forms becoming much lighter, a dark sepia; but I know of no instance of so complete a change as the one here described, viz., a complete reversion to the normal colour from a pure white. 4. The Specific, Validity of Arion fuscus, Midi. Through the kindness of Signor Pollonera, I was able in 1892 to examine specimens of this species, and from the slight differences I was able to detect in the form of the generative organs in these specimens, I was inclined to regard it as a variety of A. subfuscus, Drap. (7). Since then I have been able to make a more careful examination on some better material, for which I am indebted to the kindness of Herr Joseph F. Babor, of Prague University ; and I a m of now of opinion that, from the differences in the form of the generative organs, it must be regarded as a distinct species. ARION FUSCUS, Midler, 1774. Limax fuscus, Midler, Verm. Plist., 1774, vol. ii. p. 11. Arion fuscus, Morch, Vidensk. Medd. naturhist. For. Kjoben-havn, 1863, p. 273. Prolepis fuscus, Malm, Skand. Land-Sniglar, 1870, p. 43, pl. ii. fig. 4. Arion rufus (partim), Westerl., Expose critique Moll. Suede et Norv., 1871, p. 32. Arion citrinus, Westerl., Expose critique Moll. Suede et Norv., 1871, p. 35. Arion stabllel, Poll., Atti Ace. Sci. Torino, 1885, p. 28. Arion fuscus, Poll., Atti Ace. Sci. Torino, 1887. This species is much smaller than A. subfuscus, with the bands on the mantle distinct; the lines on the foot-fringe vary from dark |