EXTINCT ANIMALS 



this earth, with very Uttle change in form, ever 

 since the Lower Cambrian times. 



Another class of fossils which are equally 

 ancient are the Trilobites (Fig. 200). These 

 are well-marked forms with ringed or jointed 

 bodies divided very often into three longitudinal 

 lobes ; hence the old name Trilobites. An 

 immense number of different kinds of Trilobites 

 are known and classified, but they ceased to exist 

 in the Permian period (see Table of Strata, p. 60). 

 For a long time the legs of these creatures w^ere 

 unknown ; they have only been found within 

 the last ten years. Mr. Beecher, of the United 

 States, discovered them in one particular kind — 

 the Triarthrus becici (Fig. 201). Some people 

 consider these animals to be allied to the wood- 

 lice or other crustacean shrimp-hke forms now 

 living. But it seems most probable that they 

 were a primitive marine group allied to the 

 scorpions, spiders and king-crabs (the Arachnida). 



It is a fact of very great significance that the 

 earliest fossils yet discovered are the remains of 

 very highly developed animals, by no means 

 near the beginning of animal life. It is indeed 

 a reasonable supposition that the earliest forms 

 of animal life must have preceded the Cambrian 



274 



