TEREDO. 113 



however to be no more reason for classing these 

 shells with the multivalves, than Turbines and 

 others, which possess an operculum, with the 

 bivalves. The only difference between the lid of 

 the Teredo and that of a Turbo is, that the one is 

 constructed of four pieces, the other of a single 

 disk. These pieces cannot constitute the shell, 

 because the animal cannot be said to inhabit them, 

 as it does the testaceous tube. Neither is there 

 any analogy between them and the accessary 

 valves of Pholas. 



At first sight, the Teredo may easily be mistaken 

 for a Serpula, and m many cabinet specimens the 

 valves are lost. There are, however, but three spe- 

 cies of the former genus at present known, and 

 their external characters are soon to be dis- 

 tinguished. The first, T. navalis, which is the 

 most common, is much more thin and brittle than 

 Serpulae in general, especially towards the smaller 

 end. 



The name Teredo, or ngn^ s is derived from 

 r&g'sw, to bore, and is sufficiently descriptive of the 

 mode in which all the species effect their settle- 

 ment. 



