242 Of the Out*Animal. 
. 1 
con flan tly (huts upon being diflurbed, nor 
opens again until after having been quiet for 
fome Time. Its Appearance when fhut is 
pictured at fig. 1. 
The Shell is fo exquifitely thin, and con- 
fequently fo very tranfparent, as to be tra¬ 
ced out, when fhut, only by a faint Line 
on the Back, where the Cardo or Hinge 
makes fome additional Thicknefs ; but when 
open, the Edges of both its Sides may be 
diflinguifhed plainly. The two Ends of 
the Shell can open, whilfl the middle Part 
remains clofed, and in that Condition it is 
like the Pholas and fome Species of the 
Chama but differs from them, in being 
able to fhut both Ends and alter the FL 
gure of its Shell, which they cannot do. 
This probably is performed by Means of 
certain Articulations in the Shell, near its 
Extremities, which are too fine to be dif- 
cerned. When thefe Ends are open, the 
Creature frequently thrufls out, at each, a 
cylindrical flefhy Part, (as at fig . 2.) which 
may be fuppofed the Head and Tad ; but 
their Minutenefs renders it hardly poffible 
to difcover any Difference between them. 
In this Pofture it is probable the Creature 
feeds, on that Provifion the Water brings ; 
though it depends not wholly on fuch Ac¬ 
cident, for it can change its Place by Jerks, 
or Leaps, which it makes by the Adfion 
of fome firong Mufcles in the two protruded 
Parts, 
