132 UNIVALVES. 



with the surface perforated. Near the extre- 

 mity 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 con- 

 sidered 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 conse- 

 quently placed amongst the univalves. The 

 name is derived from the Greek rcpeu (tereo) I 

 bore, expressive of the manner in which the 

 animal is supposed to effect a settlement in 

 different 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 



