VERMES. 
267 
Fig. 220.—Polyzoans: 1. Hornera 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 a 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 
Fig. 221.— A Bracuiopod (Terebratulina 
septentrionali*). 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. 
