^B. eburneus^, the ivory barnacle. This species, like /B. balanoides/, is a very common barnacle, and is found on all kinds of submerged woodwork, whether fixed or floating. It is also found on the carapace of [pg256] crabs and /Limulus/, and on mollusks. It is chiefly found on objects below low-water mark. It ranges from Massachusetts Bay to Florida. It is easily distinguished from the preceding by its low, broad form and shelly base. The shell is smooth and circular at the base, and inclines backward, forming an oblique cone with a triangular opening; the plates terminate in points at the summit and incline backward, the last one forming a kind of beak. The operculum is pyramidal; two of its valves have both transverse and longitudinal lines well defined at the base, and are coarsely toothed at the edges; the posterior valves are slightly grooved across. ^B. rugosus^ (Gould), ^B. crenatus^. Shell white, cylindrical, somewhat conical, rugged, the summit usually as broad as the base; height often greater than diameter; aperture diamond-shaped, plates ending at the summit in acute spreading points, the posterior plate folded and curved like a beak; plates rough, with coarse, irregular ribs; valves of the operculum at the summit acute, with diverging points; the points striated. Found on shells and stones in deep water and also on bottoms of ships. ^B. geniculatus.^ Shell dirty greenish-white, cone-shaped; aperture about the size of base; shell-plates triangular, unequal in breadth, and with alternate large and small ribs; the smaller ribs compressed and roughened on the edges by the conspicuous lines of growth which run across them; depressed areas between the plates marked with fine cross-lines; front valves of the operculum have coarse plated ridges, which incline over one another and are crossed by fine radiating lines; diameter at base one to one and a half inches; height two thirds the diameter. Found on pecten shells, and abundant off the coast of Maine. ^B. tintinnabulum.^ Shell pink to purplish, conical, with six triangular plates, which are grooved, forming unequal ribs, and crossed by distinct lines of growth; spaces between plates crossed by lateral lines; posterior valves of the operculum longer than the others and curved forward, resembling the beak of a bird of prey; diameter at the base one inch; height one and a half inches. Found in warm waters and on vessels from the South. SUBORDER ~RHIZOCEPHALA~