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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 Gasterops is depo- 

 sited 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 dis- 

 sepiment ; base pierced with small scattered perforations ; end in- 

 closed 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 climates. 



The perfect specimens of Chcena mumia are covered with a thin 

 external coat (sometimes covered externally with particles of sand and 

 Foraminifera, which are imbedded in its surface), which is only par- 

 tially attached to the general substance of the tube by thin lines, 

 concentric with the lines of growth, leaving the rest of the coat 

 separated from the surface of the tube by a distinct hollow space. 



In some specimens, as those in the British Museum from Mozam- 

 bique, the attached part of the outer coat is in nearly concentric 

 ring-like transverse lines round the tube, leaving a more or less 

 complete hollow ring between each attached portion. In others, as 

 that from the Philippines in the same collection, the attached portion 

 of the outer coat is oblique and interlaced so as to leave only narrow, 

 elongated, oblong, hollow tessellated interspaces on the surface, which 

 are acute at each end. 



I am not certain that these characters are permanent ; but if so, 



one may be called Chcena annulosa, and the other Chcena tessellata. c 



In the latter the outer coat is simple and smooth externally. In 

 the specimen from the Philippines the tube is covered with a close 

 coat of sand and a few Foraminifera, which are deeply imbedded in 



