35 ) 



CHAP, XV. 



BIVALVES: 

 ARCAJ Ark. 



Q. Is not the Area easily to be distinguished 

 by observing that the shell is inequi valve, and 

 that the hinge is furnished with numerous sharp 

 teeth, alternately inserted between each other, 

 and most frequently placed in a longitudinal 

 direction on the hinge ? 



A. This arrangement is peculiar to the Area. 

 You will also observe that in many species the 

 Area lies flatly between the remote beaks ; that 

 it is horizontal, or a little inclined; and also 

 covered with the ligament in a manner peculiar 

 to this genus. 



Q. Are the shells generally alike in their 

 forms ? 



A. No : they vary considerably. Some are 

 oblong, others eared, and the surface is gene- 

 rally covered with a rough cuticle, or beard, 



