1 68 



ANNULOSA. 



which ranges from the Upper Cambrian to near the summit 

 of the Lower Silurian Rocks. 



2. OLENID^E OR PARADOXID^E. Character- 

 ised by having long bodies, with numerous 

 free thoracic segments (from eight to twenty- 

 three in number). The caudal shield is small, 

 and generally consists of very few segments. 

 The pleurae are mostly prolonged into longer 

 or shorter spines, which are directed back- 

 wards. The family includes some of the 

 largest of the Trilobites, and is mainly char- 

 acteristic of the " Primordial Zone " (Upper 

 Cambrian). It occurs, however, in the lower 



Fig. 114. Parado.rides Micntac (?), Upper Cambrian. After Dawson. 



Silurian, but appears to die out in the Caradoc period. The 



