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prismatic structure, which are so closed at the bases : in one speci- 

 men the closing septum is uniformly convex, and like the tube-struc- 

 ture ; in the other the septum is divided into two equal portions by a 

 transverse groove or depression ; but on neither of the specimens can 

 I observe any traces of the septum being formed of two plates over- 

 lapping in the middle like the septum of Furcella. 



The calcareous tubes of Septaria, mentioned by Home, Phil. Trans. 

 1806, p. 27b, Dillwyn, R. Shells, ii. p. 1088, and in the 'Mag. Nat. 

 Hist.' 1838, p. 408, as having a succession of Septa, proved on re- 

 examination, Mr. Woodward informs me, to be the shell of Vermeti. 



The character of the Family Teredinidce is, that the animal 

 always lives in a tube ; that it is provided with two appendages, 

 one ou each side of the siphons called palettes, which differ consi- 

 derably in structure in the different genera ; and that the front of 

 the body of the animal over the mouth is encased in two very small 

 valves like those of a Pholas in structure and form, but in a more 

 rudimentary state of development ; the tubular case of the animal, 

 apparently taking the place or being in fact a great development of 

 the dorsal additional shelly plate usually found more or less deve- 

 loped in the different genera of Pholadidce. 



Now it is clear that by Pallas, Home, and Messrs Adams referring 

 this shelly tube to the genus Teredo, they believed that it had all 

 these peculiarities. 



I was, therefore, very much pleased when a perfect specimen of 

 this interesting genus came into my hands yesterday, to believe that 

 I might have the opportunity of bringing before the Society the pa- 

 lette and valves of this genus, which until now have been desiderata, 

 especially as the sound made by shaking the tube showed that some 

 shelly pieces were contained within it. 



But on making a small aperture on the side near the base of the 

 tube to examine the structure of the valves, I was astonished to find 

 that, though the genus had two of the characteristics of the family 

 of Teredinidce, it wanted one of them ; the plates within were 

 only the palettes, which are simple and somewhat like those of the 

 more common Teredo norvegica, and that there were no proper 

 shelly valves, not even any rudiments of them ; and that the animal 

 forms a genus in that family which has the abnormality of wanting 

 the true shelly valves which are so universal in the Conchifera. 



The reason of this absence may be explained by the fact that the 

 animal does not require them to protect its head and nervous centre, 

 living as it does in a soft sandy mud ; while they are required in 

 Teredo and the allied genera which have to bore their way into hard 

 wood or stone to form the hole that is to be lined with the shelly 

 tube. 



Sir Everard Home in his ' Lectures,' when describing the animal of 

 Teredo navalis (ii. t. 81), refers this shell-tube to the genus Teredo, 

 and gives a very good figure of the palettes, or as he called them, 

 "operculum," of it (tab. 81. f . 4 & 5), but he was not aware of 

 this absence of the shelly valve; for he figures what he considers 

 the "boring shell of the same Teredo" (fig. 6): but what he has 



