Mussel and Cockle. 101 
(I. cor), which is also a member of the Clam family, 
and one of the most elegantly-shaped shells in the 
whole range of Conchology. It is a native of the 
Mediterranean and other seas of Hurope, and has 
been taken in deep water on the west coast of 
Ireland. We complete this group with a represen- 
tation of the curious Arcade family, or Ark shells, 

as they are commonly called, because one of the 
species was thought to resemble the ark built by 
Noah. Mr. Swainson tells us that the animals of 
these shells affix themselves to other bodies by a 
particular muscle, which is protruded through the 
gaping part of the valves; they also adhere, when 
young, by means of the bissiform epidermis, or 
bissus-like outer skin: this species is a native of 
the Atlantic Ocean and the seas of Europe. The 
Antique Ark (A. antiqua) is very like the Common 
Cockle, being of a white colour, and heart-shaped. 
