On the Moulting of the common Lobster (_Homarus vulgaris_) and Shore Crab (_Carcinus mænas_). By S. JAMES A. SALTER, M.B., F.L.S., F.G.S. [Read April 7th, 1859.] I am induced to bring this subject before the Linnean Society, on account of the singularly perfect specimen of the thrown-off slough of a Lobster which I have now an opportunity of exhibiting, and because the process by which it was shed was witnessed and carefully watched by two competent observers--by my friend Mr. Robert Cooke, of Scarborough, a Fellow of this Society, and by the intelligent wife of the Curator of the Scarborough Museum, in an aquarium in which institution the occurrence took place. The methods by which certain of the Decapod Crustaceans cast their old shells in the process of renewal and growth have already been made the subject of observation and record. Réaumur, as early as 1712, and again in 1718, saw and described the sloughing of the common freshwater Crayfish (_Astacus fluviatilis_). It was witnessed in the common edible Crab (_Cancer Pagurus_) by Mr. Couch, in 1833. Subsequently the moulting-process was observed by Mr. Gosse, in the Spinous Spider-crab (_Maia Squinado_). Beyond these three recorded examples, I believe that the actual operation of moulting in Decapods has never been seen, though the sloughs of our common Crustacea, and the animals themselves but recently emerged from their old shells, are familiar to all marine zoologists. There is no recorded account of the moulting of the Lobster, that I have been able to discover. The Lobster from which the slough was obtained, and whose operations are the subject of this communication, was an inhabitant of a large marine aquarium in the Museum at Scarborough. The period was July 1857. The aquarium contained the ordinary assemblage of sea-shore animals, and a considerable collection of vegetation, which consisted of _Ulva_, _Fucus_, and other common sea-weeds. For two days previous to its throwing off the shell, the Lobster was observed in a very peculiar attitude, and to be very busily engaged. Its abdomen was permanently and stiffly erected and straight; while the animal, in this rigid attitude, was hard at work detaching and carrying all the soft sea-weed it could collect to one end of the aquarium, where it thus accumulated a large mass of vegetation, which was afterwards destined to become a screen and protection for its soft body. At the same time, and by the same means, a clearing was made at the other end of the tank, in which it had space for the evolutions which were subsequently necessary for the extrication of its body.