TRILOBITES AND OTHER FOSSIL CRUSTACEA. 197 



tageously work his way to Dolgelly by Tremadoc, at 

 which place he will find abundant employment for 

 his hammer. At the village of Penmorfa the slates 

 are often crowded with remains of Trilobites. Garth 

 Hill is also a capital collecting-ground. In many 

 places the Llandeilo flags are so full of Trilobites 

 that Sir Roderick Murchison gave them the name of 

 "Trilobite Schists." Perhaps the neighbourhood of 

 Builth is the best place for obtaining them. Several 

 species of Ogygia occur, associated with numerous 

 other fossils. 



The Cambrian and Silurian rocks of the Lake 

 District are not so abundant in Trilobites as those 

 of North Wales and Shropshire, although I have 

 found them in the rich fossiliferous shales of Apple- 

 thwaite Common, and on the Lancashire side of 

 Windermere chiefly Asaphus. Calymene, Homalo- 

 notuS) and others occur in the Dalton shales, of 

 Upper Llandeilo age. In the Coniston limestone, 

 also, we have Illcenus, Cheirurus^ Agnostus, etc., all of 

 them well-marked genera of Trilobites. 



In the Silurian proper (the upper Silurian of geolo- 

 gists only a few years ago) we find Trilobites reaching 

 their maximum of existence, both in genera, species, 

 and individuals ; and we have tolerably certain 

 evidence that after this epoch they began to decline 

 until they became extinct. In the loveliest parts of 

 North Wales, as at Conway, the Devil's Bridge (near 

 Pentre Voelas), Craig Hir, and at Mynydd Fronfrys, 



