[Illustration: /Chelura terebrans/, the boring amphipod.] GENUS ^Chelura^ ^C. terebrans^, the boring amphipod. This little crustacean is associated in its work on submerged timber with the isopod /Limnoria lignorum/. The excavations of the latter are narrow and cylindrical, running down into the wood, while /Chelura/ makes larger burrows in oblique lines near the surface, which give the wood the appearance of having been plowed. It is very active and destructive. It feeds upon the wood into which it burrows. Its color is semi-translucent, thickly mottled above with pink. [pg291] GENUS ^Caprella^ [Illustration: /Caprella geometrica./] ^C. geometrica.^ These very curious little animals, which are so slender as to seem like skeletons, are found in abundance clinging to hydroids, /Polyzoa/, delicate algæ, or eel-grass, or under stones in tide-pools. They resemble in color, and often in form, the objects on which they live. Holding on by the posterior feet, they extend the body out rigidly or sway it about, so that they resemble little sticks or branches, and often escape detection. In walking, they bring the hind feet up to the front ones, doubling the body into a loop like the canker- or measuring-worm. The appendages on the anterior and posterior ends are furnished with chelæ and hooks; those of the middle section are rudimentary. This animal cannot be mistaken for any other. /C. geometrica/ is found from Cape Cod to North Carolina. Some of the species of this genus may be found on every coast. SUBORDER ~ISOPODA~ The isopods have an elongate, flattened, but more or less arched body, composed of seven thoracic segments and a short abdomen of six segments. The six segments of the abdomen are smaller than those of the thorax, and are often more or less united, sometimes into a single piece with scarcely any trace of division above; but the number of pairs of appendages is generally six, showing the composite nature of the apparently simple organ. The last segment, or telson, is broad and has a pair of modified appendages. The seven thoracic legs are not all equal, as the name would imply, but vary greatly in different species. As a rule, they are adapted to walking or attachment, and in the female some have delicate plates which form brood-pouches. The swimming-feet fold under the abdomen, and in some species are inclosed by the first pair, which are large and plate-like, and form a complete cover for the others. The isopods are a large and widely distributed order, varying in size, and are inconspicuous because they cling closely to objects. They are retiring in habit, though extremely ferocious.