The Pogge, _Aspidophorus cataphractus_, is a singularly formed fish that might be added by way of experiment. The plate-armour in which his body is clothed runs in regular longitudinal lines, showing eight sharp ridges, running from head to tail, that have a singular and unfish-like appearance. In confinement, however, he does not display himself to advantage, generally lying near the bottom of the Aquarium. The beautiful crimson maculations of the Ancient Wrasse, _Labrus maculatus_, render him a very desirable tenant; but his size—small specimens being eight or nine inches long—causes him to be inconvenient; and, moreover, he is difficult to manage, and would probably require altogether a special treatment. One of the smaller Wrasses, however, _Crenilabrus cornubicus_, is a desirable guest; his minute size, and varying and often gay colours, rendering him very attractive. He is an active and eager searcher for food, but never takes any loosely floating object, only darting at and detaching such atoms as are attached to the different species of Algæ. The Pipe-Fish, _Syngnathus acus_, is interesting in the tank, and also the two-spotted sucker, _Lepidogaster bimaculatus_, a prettily coloured and curious little fish, which has the faculty of attaching itself to the side of the tank, or any other hard flat surface, by means of two singularly-formed ventral fins, which act like the leather suckers by means of which boys enjoy the sport of lifting heavy stones at the end of a string. The spawn of this fish is like tiny amber beads, and is attached to shells and other substances. Among the Crustacea fitted for an Aquarium, the common Prawn, _Palæmon serratus_, holds the first rank. In the first place, his cleansing properties, in devouring all decaying animal matter, are most important. But not less interesting are his graceful movements: Now, he steals stealthily over the pebbles or the fronds of the Algæ, with his long, slender, hair-like horns in gentle motion, with all the seeming wariness of a cat (the resemblance being increased by candle-light by the fiery glare of the eye); next, leaving his walking apparatus, or legs, inactive, he uses only the swimming members, which are larger and flatter, and bordered with a compact fringe; agitating these instruments with beautiful regularity, he rises in the water with graceful ease (see Plate VI.), his semi-transparent body, as he rises, giving to his appearance a strange and somewhat apparition-like aspect, which has caused him to be compared to a marine spectre.