THE LOWER SILURIAN PERIOD. 



lO/ 



in later periods, they are pre-eminently characteristic of the 

 earlier portion of the Palaeozoic epoch. 



The Ringed Worms (Annelides) are abundantly represented 

 in the Lower Silurian, but principally by tracks and burrows 

 similar in essential respects to those which occur so commonly 

 in the Cambrian formation, and calling for no special com- 

 ment. Much more important are the Articulate animals, rep- 

 resented, as heretofore, wholly by the remains of the aquatic 



Fig. 47. Lower Silurian Crustaceans, a, AsapJnis tyrnnnns, Upper Llandeilo ; b, 

 Ogygia. Btichii, Upper Llandeilo ; c, Trinuclcits concentricus, Caradoc ; ti, Caryocaris 

 Wrightii, Arenig (Skiddaw Slates) ; e, Beyrichia complicata, natural size and enlarged 

 - i~.,j~:i,, -._j /^ _-. r r>:-.-, : _ _ J *,_ - __-...= 



'data, Caradoc : 



Jpper Llandeilo and Caradoc;/, Ptzmitia str 



^alymene Blumenbachii, var. brevicapitata, C 



Becki (Utica Slates), United States ; i, Shield of Leperditia Canadensis, var. Joseph- 

 iann, of the natural size, Trenton Limestone, Canada ; j, Tl 



, Head-shield of 

 thrns 



(After Salter, M'Coy, Rupert Jc 



: ^. 



adoc ; h, Head-shield of Ti 

 ditia. 

 j, The same, viewed from the 



and Dana.) 



group of the Crustaceans. Amongst these are numerous little 

 bivalved forms such as species of Primitia (fig. 47, /), Bey- 



