TEREDO. 



mostly incomplete, vaulted septa; its anterior (posterior) 

 extremity being terminated by two other, more slender 

 tubes, which are not internally divided. Thus we find 

 that in the shelly tube itself, and in the position ot the two 

 valves with respect to that tube, his descriptions of the 

 three genera accord ; and that his dependence for a cha- 

 racter to distinguish Septaria from Teredo is placed upon 

 the vaulted septa of the former^ which, however, to our 

 certain knowledge, occur more frequently in Teredo than 

 in Septaria. With regard to Lamarck's Fistulana gre- 

 gata, it appears to us to difler from his descriptions of 

 Teredo and Septaria only in having the lower end of the 

 tube closed ; in this regard, however, we shall find that 

 It disagrees neither with Septaria nor Teredo, both of 

 which occasionally close the lower end of the tube; for 

 particular proof of this fact we refer to Mr. Gritiith's and 

 Sir Everard Home's papers on the subject in Philosophi- 

 cal Transactions for 1806, part 2, where also will 

 be found a detailed anatomical description of the 

 animal. The always more or less double posterior aper- 

 ture of the tube, closed in different species by variously 

 formed double opercula^ together with the resemblance 

 in general characters above pointed out, seem to us there- 

 fore sufficient reasons for uniting Fistulana gregata, and 

 the Septaria of Lam. with Teredo ; of which we shall now 

 give the generic character. 



Shell orbicular, equivalve, inequilateral, with a 

 subalate process in front, gaping at both extremities, the 

 anterior opening angular at the back, the posterior 

 rounded in front. Anterior muscular impression placed 

 upon the subalate process. An elongated tooth is con- 

 spicuously seen curved out from under the umbones 

 within each valve. With this shell, which contains the 

 anterior extremity of the animal, it perforates wood in 

 an irregular manner to a considerable depth, lining the 

 perforations as it proceeds with a calcareous, proportion- 

 ately elongated, accessory tube, which is seldom closed 

 anteriorly, but has for the most part a round aperture, 

 and which is divided posteriorly into two tubes, which 

 can be closed at the will of the animal by two palmate, 

 sometimes pennated opercula. 



