LECTURE XI. 
I'Sl 
or Great Clamp Shell, as it is called, sometimes 
measuring more than three feet in length, and 
weighing upwards of five hundred pounds. The 
inhabiting animal very much resembles an oyster 
in appearance, and is said to furnish food sufficient 
for one hundred persons. Specimens of this gi- 
gantic shell in its full grown state are not very 
common in collections, on account of their incon- 
venient size ; those being preferred which are ia 
their small or young state 5 but in very large 
collections, as in the British and Leverian Mu- 
seums, they may be seen to great advantage ; par- 
ticularly in the latter, where there is a single 
valve of this shell weighing, I believe, at least 
three hundred pounds. 
The concluding genus of the Linnecan Bivalve 
Shells is the Pinna^ the animal of which is consi- 
dered by LinnEeus as allied to a Limax or Slug, 
and consequently to the Snail tribe also. Some of 
the species and varieties of Pinna are very large 
shells, of a thin structure in proportion to their 
size : and they are generally affixed to rocks or 
other objects by a large tuft of very fine but 
strong silken fibres or threads, which the animal 
has the power of forming, by thrusting out a kind 
