374 SEA-PINNA. 



siting over them a great quantity of its pearly calcareous matter, and 

 thus forms so many pearly tubercles over them. The practice how- 

 ever is, I believe, considered as not of importance sufficient to make 

 it an object of gain, but rather of mere curiosity ; the pearly tuber- 

 cles thus obtained being of inferior beauty to those more naturally 

 produced. 



[Shaw, 



2. Great Clamp Shell, 

 Chama Gigas. Linn. 

 This is by far the largest and heaviest of the testaceous tribes. 

 The animal, and even the shell itself, has a considerable resemblance 

 to an immense oyster. The shell is plated, however, with arched 

 scales ; the posterior slope gaping with a crenulate margin. It is 

 an inhabitant of the Indian Seas, and has sometimes been found 

 of more than three feet long, and five hundred pounds in weight ; 

 the fleshy part, or inhabitant, large enough to furnish a hundred 

 and twenty-seven men with a good meal ; and strong enough to cut 

 asunder a cable, and lop off men's hands. Specimens of this shell 

 in its full growth are not very common, from its being unwieldy ; 

 but they may be seen in the British Museum. 



[Lister. Klein, Editor. 



3. Sea-Pinna. 

 Pinna rudis. Linn. 



The animal in this genus of shell-worms, is considered by Lin- 

 naeus 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 of pointed trunk, 

 with which it touches the object it wishes to adhere to, and by re- 

 tracting it, forms a glutinous thread ; and, by the repetition of this 

 motion, forms the whole tuft by which it is fastened. 



The large sea-pinna, or pinna rudis, is a curious instance of this. 

 This shell is brown externally, with a slightly iridescent silvery cast 

 within ; of a lengthened shape, with a very narrow base, and dilated 



