^O. agilis^, the beach-flea. These little crustaceans exist in countless numbers under the masses of sea-wrack on the beach. When disturbed they jump about with great agility by means of the last three pairs of abdominal feet, which are adapted to this purpose. In color the animal is brown and much resembles the decaying seaweeds among which it lives and upon which it probably feeds. The antennules are short, the antennæ long, on two long, jointed bases. The second pair of feet in the males terminate in chelæ. The last abdominal appendages are stiff and pointed backward. The abdomen is curved under. The length of /Orchestia/ is half an inch or less. Some species occur on all beaches. /O. agilis/ ranges from New Jersey to Greenland. GENUS ^Talorchestia^ ^T. longicornis^ (^Talitrus longicornis^). This species is similar to Orchestia agilis, but is about an inch long when mature and of a paler [pg290] color. It jumps like the latter, but not so strongly. It is found among the weeds and burrowing in the sand a little below high-water mark. The wet sand is often completely filled with its holes. It can be distinguished by its very long antennæ. Another species, ^T. megalophthalma,^ is distinguished by its shorter antennæ and very large eyes. Both of these species are grayish in color and closely resemble the sand. Found from Cape Cod to New Jersey. GENUS ^Gammarus^ [Illustration: /Gammarus locusta/, the scud.] ^G. locusta.^ The animals of this genus are among the largest of the amphipods. The males are larger than the females, sometimes being one and a half inches long. They are abundant under stones and /Fucus/ at and near low-water mark. Although much larger than the beach-fleas, they otherwise resemble them. They do not jump like the former, but move rapidly, lying on the side, and in water swim with the back downward. Two pairs of the thoracic feet are chelate, and three pairs are longer than the others. The feet on the last segments of the abdomen are stiff and turn sharply back, forming a part of the tail, which is used most effectively in locomotion. The antennules and antennæ are of about the same length. Several species of /Gammarus/ occur in the same range, all having the same general characteristics; some have but one pair of chelate feet; the antennules are usually shorter than the antennæ; the females of all the species have no chelate feet. /G. locusta/ ranges from New Jersey to Greenland. The color is generally reddish- or olive-brown. ^G. annulatus^ is found in the same places, but usually a little higher up on the beach; it is lighter in color, and has dark bands with red spots on the sides of the abdomen. ^G. mucronatus^ occurs from Cape Cod to Florida. ^Melita nitida^ is a smaller slate-colored amphipod found in some places; another is ^Mœra levis^, which is whitish, with black eyes.