A ''Living FossiT 



223 



as were the hard coverings that prevailed among some 

 of their contemporary creatures. 



One of those creatures was the trilobite. And, in- 

 deed, its enduring remains are among the oldest of all 

 undoubted and definite organisms found in the primor- 

 dial rocks. The general form of the trilobite is not 



unlike that of the familiar terrestrial isopod crustacean 

 called the "sow bug." After the manner of the sow bug 

 it was able to roll itself up into a ball, and in this posi- 

 tion its fossil has often been found. Formerly the two 

 were thought to be related, but, notwithstanding cer- 

 tain of its crustacean characteristics, the trilobite has 

 in recent years been classified with the Arachnida, a 

 group including the spiders and scorpions. The truth 



