30 EXTINCT MONSTERS. 
body, and only the eyes peep out of the mud. It will crawl and 
wander about by night, but remains hidden by day. Some of 
them are of large size, and occasionally measure two feet in 
length. They possess six pairs of well-formed feet, the joints of 
which, near the body, are armed with teeth and spines, and serve 
Fic. 2.—Silurian merostomata. 
1. Stylonurus. 2. Eurypterus. (After Woodward.) 
the purpose of jaws, being used to masticate the food and force 
it into the mouth, which is situated between them. 
Now, this fact is of great importance; for it helps us to 
understand the use of the four pairs of “ jaw-feet” in our Sea- 
