172 THE MEANING OF EVOLUTION 
animals in this early Paleozoic time. These creatures 
had bodies jointed like the tail of a lobster. They 
were wide and flat, instead of narrow and rounded 
like a lobster, and each joint of the body was highest 
in the middle and distinctly lower at the two sides, 
thus forming three regions along their backs. This 
structure gives to these creatures the name of trilo- 
bites. These animals were the kings of the early 
ocean. They had an interesting habit of curling up 
nose to tail before they died, and, as a result, a large 
proportion of all the trilobite fossils we find are curled 
in this peculiar manner. 
After these forms the most abundant fossils we 
find in Silurian times were creatures that at first sight 
looked as if they might be related to the clams. These 
are known as lampshells, because one shell projects 
beyond the other and curls up at the tip so as to re- 
semble the clay lamps which are dug out of old Roman 
towns. The lampshells also have nearly disappeared 
in modern times. Simple creatures belonging with 
our present crab and snail had begun to make their 
appearance, but they were not as abundant as we find 
them later on. 
The third group of the mollusks to which the nau- 
tilus and squid of to-day belong is very abundantly 
represented in the Silurian by fossils with coiled-up 
shells. As for the plant life of the time, it is exceed- 
