Many of this order construct tubes in which they live permanently. Some species of both /Sedentaria/ and /Errantia/ have habits pertaining to the other. These worms are without a protrusible pharynx and without jaws. The body is usually divided into two or three sections by segments and appendages of different forms. They have hair-setæ on a limited number of segments only, varying with the species; the remaining segments have /uncini/, or hooked comb-like rows of setæ, which are very small, but often crowded in bunches. Uncini exist also on segments having hair-setæ. Parapodia are often lacking on the posterior parts and are usually without cirri. The gills are usually confined to the anterior end and are sometimes represented by tentacles around the head. The different species have characteristic tubes, formed by mucus secreted by epidermal glands. Sometimes the mucus hardens, making a parchment-like tube; again it cements together grains of sand, or bits of shell, seaweeds, etc. Some species secrete [pg181] calcareous tubes; these are often found on rocks, in coral, and in the shells of mollusks. The anterior end of the body is more highly developed than the posterior end. FAMILY ~SPIONIDÆ~ GENUS ^Nerine^ ^N. agilis.^ Two to three inches long; slender; somewhat flattened at the anterior end; head conical and sharp; the two tentacles about one half of an inch long; four eyes; color reddish-brown, light green on the sides; gills red; tentacles greenish-white. It burrows with extreme rapidity and lives on exposed beaches near low-water mark. ^N. coniocephala.^ Two and a half inches long, one sixteenth of an inch in diameter; head conical; body flattened on the dorsal side, round on the ventral side; has two long tentacles turned backward and a membrane on the gills of the anterior segments; gills red; bristles long and numerous. FAMILY ~CIRRATULIDÆ~ Worms of this family have a cylindrical body, more or less attenuated at each end; segments similar throughout; many segments with long, filamentous cirri which act as gills; and a conical head. They live in burrows. GENUS ^Cirratulus^ [Illustration: /Cirratulus grandis./] ^C. grandis.^ Four to six inches long; head acute; segments numerous, short, and distinct; color dull yellow, or orange, to brown, often iridescent beneath; ventral surface somewhat flattened. Numerous long, filamentous, red to orange-colored cirri extend nearly the whole length of the body and act as gills. It is common in sand and gravel at low-water mark from Cape Cod to New Jersey. [pg182] FAMILY ~TEREBELLIDÆ~ The body is cylindrical and largest on the anterior end; there are one to three pairs of more or less branched gills on the anterior end, and the ventral surface of the anterior segments is thickened by glands which secrete mucus for tube-building. These gland-spaces are called /shields/. GENUS ^Thelepsus^