172 THE MEANING OF EVOLUTION 



animals in this early Palaeozoic 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- 



