132 UNIVALVES. 



this part is always even with the surface per- 

 forated. Near the extremity of the animal's tail 

 are situated the two lanceolate valves ; they seem 

 to perform the office of flood-gates, admitting or 

 excluding the water as necessity may require. 

 Linnaeus considered that the valves placed at 

 both ends, were of the nature of opercula, and 

 that the tube was the shell of the animal, which 

 he consequently placed amongst the univalves. 

 The name is derived from the Greek repeu (tereo) 

 I bore, expressive of the manner in which the 

 animal is supposed to effect a settlement in dif- 

 ferent substances. 



TEREDO Navalis. 



COMMON SHIP-WORM. 



Specific Character. Shell thin, brittle, straight, 

 or flexuous, tapering; inside smooth, pervious"; 

 the smaller end thick and strong, furnished with 

 plates or laminae, which contract that part con- 

 siderably, and leave a very small opening ; the 

 anterior valves attached to the head of the 

 animal are of a hemispherical form, brittle, thin, 

 finely striated, and covered with a light brown 

 epidermis ; in each there is a long flat curved 

 tooth projecting inwards. The tube is white, 

 sometimes a foot long, seldom so long as the 

 animal; the foreign specimens exceed greatly 

 in size those found in England. 



This singular animal has proved exceedingly 



