226 OUR COMMON BRITISH FOSSILS. 



latter and by them this group of fossils were called 

 Lampades. 



The structure of the shells of Brachiopoda (as 



Fig. 198. Cranies, showing exterior and interior of shells. 



Dr. Carpenter has clearly shown) is different from 

 that of the bivalves or Lamellibranchiate mollusca, 



Fig. 199. Strophomena depressa, showing exterior and interior of valves (Silurian). 



although it represents one stage in the formation of 

 the shells of the latter that of the outer layer. 



Fig. 200. Stropkomena Fig. 201. Rhynchonella pugnus 



rugosa. (Carboniferous limestone). 



Owing to the large size of the " arms " (as they are 

 still technically called) of most of the Brachiopods, 

 the interior of the valves contain remarkable struc- 



