174 OUR COMMON BRITISH FOSSILS. 



CHATTER VII. 



TRILOBITES AND OTHER FOSSIL CRUSTACEA. 



To a young and enthusiastic geologist there is no 

 class of fossils to which so much interest is attached 

 as the Trilobites. They are extremely elegant objects, 

 and are easily identified. Their strict limit to the 

 primary rocks makes them geologically valuable as 

 means of identifying strata. Even non-geologists 

 remember their glib, half-scientific, half-popular family 

 name, and will occasionally air it as if it were the 

 complete key to palaeontology. A good collection 

 of well-arranged trilobites looks better in the cabinet 

 than perhaps any other fossils. There is such a 

 variation from the leading type that one cannot 

 wonder the number of genera should be so great. 

 No two are externally alike, and the deviation is 

 sometimes so extreme that the Trilobites are no 

 longer trilobed. 



Trilobites are among the few fossils which possess 

 the associations of folk-lore. Ammonites and Encri- 

 nite stems, Gryphea and Cycadites, share with them 



