181 



Serpula polythalamia, — Lin. 



These are generally of considerable size ; but Lamarck 

 is of opinion that the}', perhaps, should not be separated 

 from the preceding genus. 



5. Teredina. — A cylindrical, tubular, testaceous sheath, 

 closed posteriorly, and showing the two valves of the shell 

 at the open anterior extremity. 



Fistulana personata, Ann. du Mus. Vol. vii. p. 429 ; 

 Vol. xii. PI. xliii. fig. 6. 7. Organic Remains. Vol. iii. 

 PI. xiv. fig. 10. 



6. Teredo — is the genus in which Lamarck has disposed 

 T, navalis, the ship piercer. 



Mr. Sowerby, who has considerably illustrated this 

 genus, describes it as "a bivalve, gaping; back and posterior 

 side closed by membrane or shelly valves terminating an 

 accessory shelly tube ; hinge with one tooth in the right 

 valve ; a long free process arising from the beaks contained 

 in each valve. 



" The principal valves are longer than broad, striated 

 and gaping at both sides and at the back ; in the posterior 

 side of each is a deep rectangular sinus ; in the anterior side 

 is a corresponding small rounded sinus ; the front is lan- 

 ceolate, with an internal tubercle at the extremity ; one of 

 the accessory valves lies over the beaks, and is lobed ; 

 another is trapezoidal, covering the sinus at the posterior 

 side ; it has a line down the middle where there may possi- 

 bly be an opening, or it may indicate two valves. The 

 membrane which covers the shell is extended over the an- 

 terior side, forming a taper tube, many times longer than 

 the proper shell, and strongly impregnated, at a little dis- 

 tance from the valves, with shelly matter : in the extremity 

 of this lie two spatulate valves, attached by muscles to the 

 animal, and capable of closing the aperture, in which is 

 placed a longitudinal septum ; this tube is slightly attached 

 to a tortuous passage bored in the wood by the animal, and 



