It happened on a certain occasion that my aquarium was in an unsatisfactory condition. A nasty vapour arose from the base, and diffused itself over nearly the entire vessel. My fishes disliking their usual haunts, were all spread out at full length high and dry upon a ledge of rock-work, projecting above the surface of the water. The little Soldier-Crab had managed to drag his body and heavy tail piece up the brae, hoping to breathe the fresh air in safety. His big brother was not so successful, and despite his efforts speedily came to grief. Finding he could not drag his carriage up the rock, he stepped out of the lumbering vehicle. His appearance soon became woe-begone in the extreme. In a few minutes he expired. The buckies, too, with singular instinct, had collected in a row along the dry ledge of the tank. Upon counting the numbers of my little colony, I found all right, excepting _C. mænas_; him I could not discover, and I soon began to suspect that he was defunct. No time, therefore, was to be lost, so a diligent search for his remains was instantly commenced. Fishes, Buckies, Hermits, &c., were speedily placed in safety in an extemporaneous tank--nothing else than an old pie-dish. This receptacle, when partly filled with sea-water, admirably answered the required purpose. The water in the large vase was gently run off, and on approaching the base I found, as I expected, the dismembered carcase of the crab. One leg lay here, and another there, while the body was snugly esconced beneath a stone, on which sat my favourite limpet with its curiously formed shell, profusely decorated with a plume of sea-grass and infantile _D. sanguinea_. Here, then, I thought, was the mystery explained. It was from this spot that the noxious vapour must have emanated. Of course, the body of the crab was removed; but in performing this necessary act I tilted the stone, and so disturbed the Limpet. Guess my surprise at observing the overturned shell of the Patella to be quite empty, and its former occupant lying before me a mass of putrefaction.[5] It now began to dawn upon me that I must have libelled _C. mænas_. A few moments served to confirm this opinion, for on lifting the stone, there darted out _a_--I could scarcely believe it was _the_ crab, who instantly went through a circus-like performance around the circumference of the vessel. [5] This affords an important hint to the young aquarian to watch the Patella, and occasionally to touch its conical house, to make sure the proprietor is alive and well. The reader will be prepared to learn that what I had at first observed were portions of the exuvium, which had by some means been distributed over the tank. Many months did I wait with nervous anxiety to see the exact process of exuviation, but, except in the instances I am now about to chronicle, my wishes were never gratified.