38 CLASS I. TROPIOPODA. ORDER I. BIMUSCULOSA. 



nente ; tubo accessorio longissimo, interne septis numerosis ssepe 

 cameratim diviso, extremitate antica rariiis clausa, postica in tubu- 

 lis duobus terminum habente, operculis duobus palmatis, aliquando 

 pennatis, instructis. 



Tbe marked attention which Sowerby has given to the distribution of 

 this family readily induces us to admit the propriety of his observations 

 on the Teredo, in which he successfully proves that the Septaria arenaria 

 of Lamarck belongs to this genus : its gigantic proportions are certainly 

 remarkable, but the character which is cited by the latter of the "vaulted 

 septa" is evidently common to both. 



In this genus of Tubicola the animal presents another distinct modifi- 

 cation of character ; as in Fistulana, its shell is entirely free and inde- 

 pendent of the tube, but it differs from that genus in being external. 

 From its mode of habitation it appears to have immense power of tere- 

 brating or boring, and the tube is formed by a secretion of calcareous 

 matter lining the perforation as it advances. 



The shell of Teredo may be described as orbicular, inequilateral, gaping 

 at both sides, and having a long recurved tooth standing out from be- 

 neath the umbonal margin of each valve : the accessory tube is very long, 

 and often internally divided into chambers by numerous septa : the ante- 

 rior end is sometimes, but rarely, covered over, and the posterior termi- 

 nates with two smaller tubes, which are closed at the will of the animal 

 by two palmate, sometimes pennated, opercula. 



This animal is remarkably destructive, piercing any timber that is 

 covered by the sea in every direction, and so completely intersecting it, 

 that immense piles and foundations have been quite undermined. 



Example. 



PI. XXI. Fig. 1 to 4. 



Teredo navalis, Linnajus, Syst. Nat., p. 1267. Enc. Me'th,, pi. 167. 

 f. 1 to 5. 



