286 MOLLUSCA. 



tain points; but each orifice always forms a little six-rayed star on 

 the surface. We unite them all under the name of 



POLYCLINUM. 

 Some of them are extended over bodies like fleshy crests. Others project 

 in a conical or globular mass; or expand into a disk comparable to that of 

 a flower or of an Actinia; or are elongated into cylindrical branches sup- 

 ported by slender pedicles, &c. ; or form parallel cylinders. 



CLASS V. 

 BRACHIOPODA. 



The Mollusca Brachiopoda, like the Acephala, have a bilobed 

 mantle which is always open. Instead of feet they are provided 

 with two fleshy arms, furnished with numerous filaments, which they 

 can protrude from, and draw into the shell. The mouth is between 

 the base of the arms. 



All the Brachiopoda are invested with bivalve shells, fixed and 

 immovable. But three genera are known. 



LiNGULA, Brug. 

 Two equal, flat, oblong valves, the summits of which are at the extremity 

 of one of the narrow sides, gaping at the other end, and attached between 

 the two summits to a fleshy pedicle, which suspends them to the rocks; the 

 arms become spirally convoluted previously to entering the shell. It ap- 

 pears that the branchiae consist of small leaflets, disposed around the inter- 

 nal face of each lobe of the mantle. 



But a single species, Lingula anatina, Cuv., is known. It inhabits the 

 Indian Ocean, and has thin, horny and greenish valves. 



Terebratula, Brug. 

 Two unequal valves united by a hinge; the summit of one, more salient than 

 the other, is perforated to permit the passage of a fleshy pedicle which at- 

 taches the shell to rocks, madrepores, other shells, &c. Internally, a small 

 bony piece of frame-work is observed, that is sometimes very complex, 

 composed of two branches which articulate with the unperforated valve and 

 that support two arms edged all round with a long, close fringe, between 

 which, on the side next to the large valve, is a third, simply membranous 



