TRILOBITES AND OTHER FOSSIL CRUSTACEA. 199 



called " Cave Dale " (undoubtedly an ancient cavern 

 with the roof worn off) we may find this Trilobite 

 associated with a wonderfully abundant collection of 

 other fossils. At Salt Hill, Clitheroe, in Lancashire, 

 the shales which part the limestone bands are seen 

 crowded with the evidently moulted remains of 

 Phillipsia, 



The large number of species, even of British 

 Trilobites, obtained from the various strata above 

 mentioned, are grouped into certain families. We 

 have first the Agnostidce, characterized by their small 

 size, by the head and tail being covered with two 

 nearly equal shields, and the possession of not more 

 than two body-rings. This family was eyeless. The 

 Olenidce or Paradoxldce had long bodies, with 

 numerous free segments. The caudal or tail shield 

 was small ; the side lobes were prolonged into curved 

 Spines. A large number of the more ancient genera 

 of Trilobites belong to this family. The Asaphidce 

 were tolerably large oval Trilobites, with smooth 

 carapaces, and possessed about eight body-rings. 

 Illcemis and Ogygia are included in this group. The 

 TriniLcleidce had a large head-shield, ending in two 

 long spines, one on each side. The body-rings were 

 five or six in number. The Cheimridce included seven 

 distinct genera, which had a geological range from the 

 Cambrian to the Devonian strata. The facial sutures 

 of the head-shield ended on the outer margin. The 

 number of rings or segments was eleven, and these 



