CIRRIPEDIA 



361 



of shell 4 cm. : cosmopolitan, often very numerous, especially in early 

 summer, on the North American coast, sometimes as far north as the 

 Bay of Fundy, attached to seaweed and other floating objects; Pacific 

 coast north of San Francisco. 



L. anserifera L. Stalk about as long as the body; plates radially 

 grooved; length of shell 5 cm.: cosmopolitan. 



L. anatifera L. (Fig. 570). Stalk usually as long as 

 or longer than the body; shell bluish-white; plates faintly 

 striated; length of shell 5 cm. or less: cosmopolitan; on 

 ships ^ bottoms and floating objects; the commonest species; 

 more southerly than L. fascicularis. 



2. CoNCHODERMA Olfers. Carina and terga small or 

 wanting; scuta narrow, the parts of the shell not touching 

 one another; stalk long and almost as broad as the body, 

 tapering from it to the pomt of attachment: usually 

 attached to ships^ bottoms, but also to other objects; 3 

 species. 



C. virgatum (Spengler) (Fig. 571). Length, including stalk, 5 cm.; 

 color grayish, w^ith 6 dark longitudinal bands: cosmopolitan. 



Fig. .571 



Conchoderma 



virgatum 



(Pilsbry). 



Family 3. BALANIDAE. 

 Rock barnacles. No stalk present; body enclosed in a thick cal- 

 careous shell; this is made up of a number of pieces which are joined 

 together to form a cylinder, in which the animal lies on its back with 

 the 6 pairs of thoracic feet uppermost; 2 pairs of hinged plates, cor- 

 responding to the scuta 

 and terga of Lepas, 

 close the aperture of the 

 cylinder and, on open- 

 ing, permit the legs to 

 be thrust out and sweep 

 in particles of food: 

 inerusted on rocks and 

 timbers, etc., often in 

 great numbers; about 7 

 genera and 75 species. 

 Balanus L. (Fig. 

 572). Cylindrical shell composed of 6 thick pieces joined by thinner ones; 

 basis of the shell either membranous or calcareous: about 46 species, of 

 which S occur on the Atlantic coast. 



B. balanoides (L.). The common barnacle. Base of shell mem-' 

 branous; tergum with a spur; cylindrical shell of variable shape and 



Fig. 572 — Diagram of Balanus (Darwin"). A, entire 

 shell ; B. the animal within the shell. Explanations 

 as in Fig. 570. 



