[ 234 ] 
which feem to (hut. the' valves in common niells,- 
They are however flriclly joined to this place 
during the animal’s life; which makes one think 
there is a ligament at the tail of the inhabitant, by 
which he Ihuts himfelf in. The length of the 
fheil is half a line, and its greater breadth above a 
quarter of a line. That fpecies mentioned by the 
above writers is three times longer before it comes 
to its full growth. It is hairy, though fmooth to 
the naked eye, more indented at the dopes where- 
the valves are projedling, and more deprefied towards 
the hinge ; it is opaque, and of a changeable colour. 
Some of thefe infers are of a light and others of 
a dark green, marked with an oblique ftripe of a 
lighter than the reft.' Some of thele are bright, and 
others grey and dirty ; but the down with which the 
fliell is covered, and to which the dirt (ticks, is only 
vilible with the microfcope. I have examined feveral 
of thefe, at different ages, and at different times of 
the year, and have found them all rough ; whereas- 
every one of thofe of the new fpecies is fmooth. I 
fliall call this new fpecies the white fmooth bivalve,, 
to diftinguifh it from another, the fliell of which 
is white and rough ; and from tliat of the above 
mentioned authors, which I call i\\Q fo^’dif in allufioir. 
to the dirty flaell in which it is often found. 
I have already obferved how difficult it is to dif- 
cover the fliape of the inhabitants of thefe bivalves r 
however, the tranfparency of fmooth white one, 
gave me an opportunity of examining the lateral 
part of its inhabitant with the microfcope ; and a 
happy accident, by which I catched the Jbnlid 
one at reft upon the back of its own valves, en- 
abled 
