298 Zoological Society : — 



In general the tubes of Teredo are entirely imbedded in tbe wood, 

 but sometimes, as in a specimen we have in the Museum from the 

 mouth of the River Nunn, the a})ices of the tubes of the shell pro- 

 ject as if they were produced by the animal as the shelly tube en- 

 larged beneath ; but I believe this arises from, and at least is par- 

 tially, if not entirely, caused by the surface of the wood disin- 

 tegrating and leaving the apices of the tubes exposed. In the same 

 collection are a series of the tubes of a species of Teredo, from 

 Van Diemen's Land, which are more or less covered with Serpnl(S 

 and Fei-meti ; I suspect these must be specimens which have been 

 partially or entirely exposed by the rotting of the wood in which 

 they were enclosed. 



These specimens from Van Diemen's Land, so covered viith. Serpulce, 

 also exhibit another peculiarity : in one case two tubes are parallel 

 to each other, and firmly united by the outer surface of one of their 

 sides into one body, which induced me to believe that they might be 

 Serpulce, until I examined the structure of the shell and observed 

 the simple contracted apex of the upper extremity. 



In those genera of Teredinidce which have a number of half-septa 

 across the upper or smaller aperture of the tube, forming a kind of 

 incompletely valvular structure on the sides of the siphons, or as 

 in Furcella, where the space between the siphons is entirely closed 

 up, leaving only a tube for the passage of the siphon on each side of 

 the upper cavity, these septa and the solid calcareous matter forming 

 the tubes must be deposited by the surface of the siphons them- 

 selves, as the canal of the univalve Zoophagous Gasteropods is de- 

 posited by the siphon of the mantle of these animals. 



And as the palettes or opercula, as they have been erroneously 

 called, of this family, are fixed on each side between the base of the 

 two more or less elongated siphons, in all those genera which have 

 a siphonal septum like Furcella, or lamina like Teredo at the apical 

 end of the tube, these palettes are always enclosed in the tube, and 

 cannot be exserted as they are sometimes represented. 



The character of this genus must be thus amended : — 



Furcella. 



Animal without any true shelly valves ; siphonal palettes distinct, 

 large ; apex dilated, transverse, spathulate, with a central midrib and 

 an elongated slender cylindrical base. 



Tube clavate, irregular, sometimes bent ; apex with two tubular 

 siphonal apertures separated by a broad, hard, shelly, longitudinal 

 dissepiment ; base pierced with small scattered perforations ; end 

 enclosed by two overlapping convex septa, arising from the sides 

 and completely closing the ends. 



These arched terminal plates appear to be absorbed before each 

 period of activity, and the end is again closed with similar plates at 

 each period of rest, after a sufficient elongation and enlargement of 

 the tube for the protection of the enlarged animal. Living sunk in 

 sandy mud on the shore in tropical clhnates. 



The perfect specimens of Chcena /mania arc covered with a thin 



