^L. anatifera.^ The shell is bluish-white, showing lines of growth and faint radiating lines emanating from the anterior basal angle. The upper valves are narrow; the long tips point downward, and the top is blunted, leaving a space which is occupied only by a membrane. Near the apex of the shell, at the back, is a distinct angle. The dorsal valve is broad, not much compressed, and is sometimes grooved lengthwise. The cartilage of the shell and the stalk adjoining the shell are orange-colored. The stalk is grayish-brown and the cirri flesh-colored. The stalk is from one inch to six inches long. The shell is one inch long. ^L. striata.^ Shells bluish-white; valves sharply triangular; dorsal valve compressed, forming a ridge; lines radiate from the basal angle of the lower valves and from the upper angle of the terminal valves, starting from the extreme end; the margins have a narrow edge of yellow cartilage; the stalk and cirri are of a dark slate-color; shell and stalk are each about an inch long. ^L. pectinata.^ Shell shorter and less compressed than in the preceding species; lines of growth and radiating lines distinct; a decided line [pg254] runs from anterior base to summit, a little back of the margin; terminal end broadly obtuse (truncated); dorsal valve much compressed, forming a sharp edge serrated with ten to twelve teeth and distinctly striated or furrowed. [Illustration: /Lepas anatifera./ A, the entire animal; B, anatomy. /a/, antennule; /c/, carina; /cd/, cement-gland; /l/, digestive gland; /m/, adductor muscle; /od/, oviduct; /ov/, ovary; /p/, peduncle; /s/, scutum; /t/, tergum and testis; /vd/, vas deferens; /h/, tentacles.] [Illustration: PLATE LIX. Different forms of Balanus. (After Darwin.) Cenobita diogenes.] GENUS ^Balanus^ /Balanus/ is known as the "acorn-shell," or "sea-acorn," and is found in vast numbers and of all sizes between tide-marks, incrusting rocks and the piles of piers. It also may be found attached to floating objects or to shells, or even to living animals, but its usual habitat is stationary. Unlike /Lepas/, it has no stalk, the shell being directly attached to some object. The body is surrounded by a fold of skin, to which are attached a shell consisting of six or more plates and a fourfold lid, or /operculum/, consisting of two /scuta/ and two /terga/. The operculum may be called the door, as the animal opens and shuts it at will and has complete protection when it is closed. If one taps a rock [pg255] incrusted with barnacles, and holds the ear near, the closing of the many doors may be distinctly heard.