LECTURE XI. 181 



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 gh- 

 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 in 

 their small or young state ; 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 Linnaean Bivalve 

 Shells is the Pinna, the animal of which is consi- 

 dered by Linnaeus 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 



