74 Llandeilo and Caradoc Beds. 



Sandstone or Bala beds. 19 genera and 34 species of 

 corals have been described in these lower Silurian strata, 

 among which Heliolites and Petraia are perhaps the 

 most common. 



Fragments of Echinodermata are common, including 

 Cystideans, common in the Bala Limestone, and one 

 star-fish, Palceaster Caractaci. In all, more than 40 

 genera and 200 species of Trilobites have been described 

 from the whole series of Lower Silurian British rocks, 

 among the chief of which are species of Olenus, Ag- 

 nostus, Ampyx, Lichas, Ogygia, Acidaspis, Asaphus, 

 Harpes, Ulcenus, Phacops, and Trinudeus (T. Carac- 

 taci). In the Caradoc beds alone, 23 genera and 111 

 species are known. Of bivalve shells there are 22 

 genera and 171 species of Brachiopoda, the most com- 

 mon of which belong to the genera Strophomena, 

 Leptcena, Lingula, Orthis, and Rhynchonella. 



Of the Lamellibranchiate molluscs there are 17 

 genera and 87 species known at present, prominent 

 among which are Ctenodonta, Modiolopsis, Pterincea, 

 Palcearca, and Ambonychia. Of Pteropoda there are 

 known 6 genera and 31 species, of which Theca is most 

 abundant; 16 genera and 66 species of Grasteropoda, 

 the most characteristic of which in point of numbers 

 are Euomphalus (10), Murchisonia (15), Pleuroto- 

 wia/ria, Cyclo7iema,a,rLdHolopcea. Of Nucleobranchiata, 

 Bellerophon (14). Of the Cephalopoda there are 10 

 genera and 62 species Cyrtoceras (5), Lituites (6), 

 Orthoceras (42), Phragmoceras (1), and others. No 

 fishes nor any other vertebrate animals have yet 

 been found in the Lower Silurian rocks of Wales or 

 elsewhere. 



In Cumberland the Coniston Limestone is believed 

 to be the equivalent of the Bala Limestone of North 



