VERMES. 



267 



Fro. 220. Polyzrtans: 1. ffornera lichenoides, natural size. 2. Branch of the same, 

 magnified. 3. Discopora Skenei, greatly enlarged. 



more convex ; but they 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, 

 through 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 



FIG. 221.. A Bnichiopod (Terebratulina 

 septentrionalit). 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 Brachiopod 

 (Terebratula), showing, in descending 

 order, cardinal process, dental sockets, 

 hinge-plate, septum, and loop support- 

 ing the ciliated arms. 



