CHTHAMALIN^. 



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 ; § n. s. 



320 



321 



322 



323 



324 



325 



Sub-Family II Chtliamalince. 



Chthamalus (Ranzani). Shell-valves six ; base 

 membranous, but sometimes apparently calcareous, 

 owing to the walls being bent inwards. 



C. stellatus. Fig. 324 ; n. s. 



