CHAP. VIL 



BIVALVES: 



SOL EN ; Razor- Sheath, or Knife-Handle. 



Q. WHAT are the distinguishing character- 

 istsics of the Solen ? 



A. An oblong shell gaping at both ends. 

 Hinge with awl-shaped teeth, bent backwards, 

 often double, not inserted in the opposite valve ; 

 lateral margin obsolete (indistinct). 



Q. Are the valves convex? 



A. Yes. The length of the shells in this genus 

 is another remarkable character, and many of 

 them are extremely brittle. 



Q. Is not the form of the shell beneficial to 

 the inhabitant ? 



A. It is admirably adapted to assist the mo 

 tions of the animal, which are exclusively in a 

 perpendicular direction. It makes its way through 

 the sand of the sea-shore to a certain depth, 

 and thence again to the surface in quest of food- 



