50 Mr. J. Alder on the Animal of Kellia rubra. 
another species of the same genus, the walls are closed ; yet their 
functions are surely analogous. A similar siphonal fold, though 
less perfect, may be seen in some of the Modiole: but the case 
most in point is the siphon of the zoophagous gasteropods, which 
is a prolongation and fold of the mantle similar to this, yet no 
one that I am aware of has argued that it cannot be for the sup- 
ply of water to the branchiz because it is continuously open with 
the other parts of the cloak*. 
Mr. Clark thinks my views incorrect: “ As in those bivalves 
with open mantles the currents of water enter by the great pedal 
orifice or rima magna of the mantle to aérate the branchie, and 
the greater part of the impure fluid is expelled by the aperture 
of ingress, a small portion, as before stated, passes out by the 
posterior siphonal apparatus.” Is this any more than a repetition 
of the former statement, leaving out the opening and shutting of 
the valves, and defining the purpose more distinctly to be, “ to 
aérate the branchie” ? That it has reference to the same action 
is evident from the words “as before stated.” ~ Mr. Clark must 
therefore either think that the branchial currents are produced 
by the opening and shutting of the valves, or he is confounding 
two things that are distinct. If the pedal orifice is the principal 
one by which the true branchial currents are received and ex- 
pelled, of course my observations, and the views of almost every 
author who has written on the subject must be wrong, but the 
proof requires to be brought forward in some more definite form 
than this. 
Again, Mr. Clark says, “In the mollusca with nearly closed 
mantles, only a small portion of the fluid can enter by the re- 
stricted pedal orifices ; the far greater portion must be inhaled 
by the posterior siphons ” (not necessarily by both), “ and is often 
expelled simultaneously at both orifices, as I have observed in 
Pholadidea papyracea, the most closed of all the bivalves.” This 
fact of the occasional simultaneous expulsion of water at both 
orifices seems to be the only one that Mr. Clark has satisfactorily 
ascertained from observation in this species; he might perhaps 
have added that it was accompanied by a closing of the valves ;— 
at least such is the case with the allied Pholades as I have myself 
witnessed. But this sudden ejection of water is only occasional, 
and caused by other means than the regular ciliary currents. It 
is probable that in the Pholades and some other bivalves with 
* I am sorry to have misunderstood Mr. Clark with respect to the sense 
in which he took the words branchial and anal. I did not say, however, 
that he wsed the words, but that he appeared to take them (as used by 
others) in too restricted a sense. My reason for thinking so was, that he said 
the posterior opening had “ passed for the anus,” and took some trouble to 
show that the true anus is distinct from it. 
