42 
SHELL GALLERY. 
198- 
199, 
Case 198. 
Cases 199- 
201. 
blematical. A fine series of these shells is exhibited in Gallery VIII., 
wall-case 5, in the Geological Department. 
The Myidai, popularly known as " Gapers" on account of their 
valves being open at one or both ends, have the mantle united all 
round, except where the small foot is protruded. The siphons are 
Fie:. 34. 
British Gaper (Mya truncata). 
a, foot ; b, siphon-sheath ; c, exhalant siphon ; d, inhalant siphon ; e, umbones 
or beaks ; /, anterior, g, posterior end of shell. 
very long, united almost to the ends, and covered with a coarse 
wrinkled outer skin. They bury themselves in mud and sand at low- 
water mark or in shallow water. The species are few in number, and 
chiefly from the shores of northern countries. Mya armaria of our 
own coasts is largely eaten in some parts of Europe and North America. 
The Corbulm (Case 198) have one valve larger than the other 
and are like little Mya, but the valves arc almost closed and their 
siphons are very short. 
Many of the Solenida, or Razor-shells, possess very elongated 
shells, and are remarkable for the great development of the foot, 
Fig. 35. 
British Razor-shell (Solen siliqud). 
a, foot ; b, mantle ; c, inhalant siphon ; d, exhalant siphon ; e, shell. 
which can be pointed or contracted as may be required for boring 
into sand. By means of this powerful foot the animals, when 
