158 



MOLLTJSCA. 



serves as a font in many continental churches, frequently attains 

 a weight of 500 pounds. 



Pholadidas have accessory valves in the hinge of the shell. In 

 Teredo the valves are merely appendages of the foot. In Gastro- 

 chaenidse the valve or valves are adherent to a tubular shell. 



The extinct family Hippuritidse ( = Rudistas) is characterized 

 by an inner 1-3-toothed hinge, the teeth confined to one valve. 

 It is a distinct order for some authors ; allied to Chamidte for 

 others. It is only known in the Cretaceous period. 



