62 MYlll.F. 



level with the surface of the muddy bottom in full action. 

 The mud lies closely packed against the walls of the 

 tubes, so that nothing is to be seen but the internal 

 surface of the expanded lips of the siphonal orifices 

 fringed with numerous tentacles. When it happens 

 that the surface of the water is only a little above these 

 orifices, a strong current can be distinctly seen to boil 

 up from the anal siphon, and another, with a constant, 

 steady flow, to set into the branchial one. These cur- 

 rents were quite risible to the naked eye without the 

 aid of a glass, so long as the mollusk remained undis- 

 turbed. We watched one individual for nearly a quar- 

 ter of an hour, and no interruption of them took place, 

 and it was not until the siphon was touched, that the 

 tubes were withdrawn and the current ceased to play. 

 But the siphon soon made its appearance again at the 

 surface, and the orifices once more expanding, the cur- 

 rents commenced to play as strongly as ever 



On removing these animals from their concealed abodes, 

 and placing them in a vessel of fresh sea-water, the two 

 siphonal currents were generally found in action when 

 the individuals were undisturbed. And further, on 

 placing the shell with its back downwards and the pedal 

 gape raised above the surface of the water, these currents 

 still continued to play; the excurrent and incurrent 

 being as distinctly observed as before." The authors 

 of this paper also ascertained that the currents commu- 

 nicate through minute openings in the laminae of the 

 gill-plates, which are sieve-like, filtering and collecting 

 all the nutritious particles imbibed through the inhalant 

 tube, in order that they may be carried to the mouth 

 by the labial palps. Mr. Clark opposed the above view 

 of the case, and endeavoured to prove that the water 

 was mainly, if not altogether, introduced through the 



