VERMES. 



267 



Fig. 220.— Polyzoniis: 1. Rornera lichenoides, nl\tm!l^ size. 2. Biauch of the same, 

 ranguified. 3. DUcopora Skenei, greiitly eiihivged. 



more convex ; but tliey are symmetrical, i. e., a vertical 

 line let fall from the hinge divides the shell into two 

 equal parts. The ventral valve has, in the great major- 

 ity, a prominent beak, perforated by & foramen, or hole, 

 tlirough which a fleshy foot protrudes to attach the ani- 

 mal to submarine rocks. The valves are opened and shut 

 by means of muscles, and in 

 most cases they are hinged, 

 having teeth and sockets 



A 



Fig. 221. — A Brncniopod {Terebratulina, 

 aspUntruyiuilvi). Atlantic coast. 



near the beak. The mouth 

 faces the middle of the mar- 

 gin opposite the beak; and 

 on either side of it is a long. 



Fig. 222.— Dorsal Valve of a Erachiopod 

 (Teretn-atula), showing, in descending 

 order, cardinal process, dental sockets, 

 binge-plate, septum, and loop support- 

 ing the ciliated arms. 



