181 



Serpula polytlialamia. Lin. 



These are generally of considerable size ; but Lamarck 

 is of opinion that they, 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. PL xliii. fig. 6. 7. Organic Remains. Vol. iii. 

 PL 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 



