TRILOBITES AND OTHER FOSSIL CRUSTACEA. 193 



Trilobites had generic relations with the common 

 Apus of our ditches and ponds. Sufficient has been 

 said, however, to show how large a middle space 

 the numerous family of Trilobites occupy. At the 

 one extreme they nearly touch the king-crabs and 

 at the other the aborted shrimp-parasites, as in the 

 case of Agnostus. Perhaps the living Serolis better 

 represents the average forms of Trilobites than any- 

 thing else. 



Fig. 158. Serolis Fabrtcii. Fig. 159. Under side of Serolis Fabricii. 

 a, eyes ; b, feet ; c, organs of mouth (recent). 



The Cambrian strata have recently been ex- 

 tended upwards as high as the "May Hill" group, 

 so as to include rocks formerly classed as Lower 

 Silurian. They are well represented in many parts 

 of Great Britain, notably in North Wales and the 

 Lake districts. Trilobites of various genera may be 

 met with in many localities which are usually visited 

 by tourists for the sake of the scenery alone. It is 

 one of the privileges of the geologist, that his calling 



O 



