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two lanceolate plates, or valves, one on eacli fide; a 

 little concave on the infide, and rounded at the end : 

 the office of which is to clofe the extremity of the tube 

 at the thickened part. Thefe feem to be properly the 

 fhells of the animal, being attached to it. The tubular, 

 teftaceous cafe, or fheath, which lines the hole made 

 by this animal in wood, though necelTary to its exigence, 

 appears only to be formed as an apartment, in which 

 it may move with eafe and fecurity ; for it is obfervable, 

 that no two tubes ever touch each other, although the 

 lamina of wood between thenl is frequently not thicker 

 than paper. The lube is leldom fo long as the animal, 

 as the interior part of the perforation is ufually not lined 

 with it for two inches or more : the fmaller end is always 

 even with the furface of the timber perforated, but fo 

 fmall as not eafily to be difcovered ; but fufficient to ad- 

 mit the furrounding element, and which the animal can 

 regulate by the pollerior valves. 



It has been erroneoufly imagined, that the animal 

 perforates wood by means of its anterior valves ; but 

 there is no reafon for afcribing fuch a property, becaufe 

 their fhape has been likened to an auger, when we find 

 all the PJiolas, the My tikis rugofus, the Donax Irus, and 

 many others perforate not only wood, but even the 

 hardeft lime (lone, without the affiflance of their fhells, 

 a part impofiTible to effetl it. 



It is obfervable the Teredo bores acrofs the grain of the 



Y y y wood 



