CHTHAMALIN.E. 



173 



Pyrgoma (Leach). Shell- valves united into one; 

 base cup-shaped, or sub-cylindrical; affixed to 

 corals. 



P. Anglicum. Fig. 322 ; n. s. and mag. 



Coronula (Lamk.). Shell- valves equal; walls 

 thin, deeply folded ; opercular valves smaller than 

 orifice, affixed to living Cetacea. 



C. diadema. Fig. 323 ; j n. s. 



323 



324 325 



Sub-Family II. Chthamalmce. 



Chthamalus (Eanzani). Shell-valves six; base 

 membranous, but sometimes apparently calcareous, 

 owing to the walls being bent inwards. 



0. stellatus. Fig. 324 ; n. s. 





