THE LAMP SHELLS 3403 



oldest of the Brachiopods. Indeed, if we may look upon the hinge which charac- 

 terizes the other order as a specialization, the hingeless forms are clearly the older 

 and more primitive. The shell of a Lingula is thin and horny, almost flexible, and 

 green in color. The valves are almost exactly similar, and, as we have seen, they 

 are not hinged together; and, further, the)' have no processes for the support of 

 the thick, fleshy spiral arms. No living Lingula is now found in European seas, 

 but L. pyramidata occurs on the American coasts, and another, L. anatina, in 

 the Philippines. The stalk of the former, which is nine times as long as the body, 

 does not become attached, but moves like a worm, and again, like certain worms, 

 makes tubes out of sand into which it can withdraw. The Lingulidce generally 

 live in holes in mud, the bottom of which is lined with sand. The shell-covered 

 body projects above the mud to open and feed; on being alarmed, it shuts and dis- 

 appears below the surface. The cilia at the mantle edge form a fine sieve which 

 prevents foreign particles from entering the gills. The length of life of L. pyrami- 

 data is not more than a year. The simplicity of the shell of Lingula, which may 

 best be compared with the cartilaginous structures at the anterior end of a chsetopo- 

 dous annelid, and its occurrence in the oldest strata in which Brachiopods are found, 

 seems to justify the conclusion that it stands nearest of all the class to the worm-like 

 ancestor. 



