158 Shell Life 



not so macli as half an inch during the entire life 

 of the Razor. This mode of enlargement explains 

 why the hinge occupies its singular position at the 

 extreme front of the upper margin. In the left 

 valve this hinge consists of two stout curved 

 cardinals, and one or two long hooked laterals behind 

 them and below the ligament; in the right valve 

 there is one tliin broad cardinal that fits between 

 the cardinals of the other valve, and behind it a 

 single lateral fitting under the hook of its fellow in 

 the left valve. It is remarkable how so one-sided 

 an arrangement suffices to keep the long and heavy 

 valves toofether. That it does suffice is evident on 



Pod Razor interior of left valve 



handling the empty shells ; yet during the life of the 

 mollusk the power of the hinge- teeth is greatly 

 reinforced by the adductor muscles, whose positions 

 are marked by the shaded portions in the above 

 fio^ure. 



The animal is of a pale drab colour, with a 

 yellowish, tongue-shaped foot. Except at the fore- 

 end for the passage of the foot, and a minute opening 

 on the lower surface, the mantle-edges are united 

 throughout. The siphons are exceedingly short, 

 united, and their openings fringed. At the base of 

 these filaments there are grooves in which are 

 situated pigment spots highly sensitive to light ; and 

 a shadow cast over the sands when the Razors are 



