144 Mr. W. Clark on the Animal of Kellia rubra. 
having separate apertures, as an acquittance on account of those 
parts of his observations which I have neglected to notice, and 
which, if established, will I am sure be considered by that gen- 
tleman as a sufficient answer. 
I propose to demonstrate that the water for branchial, as well 
as alimentary purposes, passes into the branchial cavity by both 
the posterior siphons, in conjunction with the pedal aperture in 
those animals in which the ventral range is sufficiently open, and 
is expelled indiscriminately in various proportions from all the 
apertures I have mentioned. 
It appears entirely to have escaped Mr. Alder’s observation that 
the posterior siphons of all bivalves have other functions besides 
the conveyance of water to the branchie, and that they are also 
furnished with most important organs of prehension, for pro- 
viding for the animal’s sustentation ; these are the tentacular 
cirrhi and cilia which clothe both the anal and branchial siphons 
of a great majority of the bivalve mollusca, to entangle and cap- 
ture the minute animalecul to be conveyed into the branchial 
cavity: how, and by what means, is this operation to be accom- 
plished? I answer, through both the posterior ciliated siphons, 
by the agency of the currents of water, which enter and thus 
enable them to deposit within the branchial walls the prey which 
each cirrhigerous siphon has captured. We cannot suppose that 
nature has furnished the siphons of the animals with organs for 
taking their prey, without at the same time providing the means 
of conveying it into the branchial cavity, and there cannot be 
any other than the passage of the water through each siphon. 
We have here irrefragable proof that both the posterior siphons 
are subservient to provide the animal with water for branchial 
and alimentary uses. 
The Pectines, Anomie, and Ostree also indisputably prove the 
fallacy of Mr. Alder’s doctrine of distinct apertures of ingress 
and egress for the branchial currents, as im these genera the 
animals have only one immense aperture, which extends nearly 
throughout the periphery of the shell, consequently the water 
can only enter into and issue from the same aperture. 
The only other point I must notice is Mr. Alder’s assertion 
that I have “ overstated ” the tidal range of Kellia rubra. What 
I said with respect to the habitat of this species, was from the 
recollections of fifteen years ago. I visited the locality a few 
days since, and again this day, with a person well aequamted 
with the coast, who called in to assist his judgement another in- 
dividual, who informed me that the rock from which I took in 
their presence Kellia rubra, is often not covered with water for a 
fortnight at a time in calm weather: therefore, as I stated in my 
last paper, the washing of the bases and sides of the rocks suffices 
