My. J. Alder on the Animal of Kellia rubra. 49 
found myself in agreement. Our opinions, however, appear to 
differ more widely that I at first expected. 
In my last letter I ventured to lay down, perhaps more broadly 
than usual, the theory of the branchial currents in the Conchifera 
as generally received* ; and confirmed, as far as my experience 
goes, by my own observations. This theory of ciliary currents, 
received and expelled by separate apertures, Mr. Clark entirely 
denies, and thinks, if I understand him rightly, that no apertures 
are specially set apart for this purpose, but that the water for 
branchial purposes flows in and out of all the openings of the 
mantle indiscriminately ;—whether by ciliary action or not, is not 
stated. 
To enter into a review of this process as applied to the whole 
of the bivalves would greatly extend a discussion already, I am 
afraid, encroaching too much upon your pages; and as I do not 
feel that I shall be able to throw any new light upon it from my 
own observations, I shall waive the general subject for the pre- 
sent and confine myself to the consideration of Mr. Clark’s ob- 
jections to my views on Kellia rubra, which he thinks it not dif- 
ficult to show are wrong. Let us, then, carefully examine the 
arguments by which this position is to be established. 
The first is thus stated :—“It must be borne in mind that the 
mantle of Kellia rubra is open from the posterior branchial shit 
to its anterior termination. The open fold in question is merely 
a prolongation of that membrane; and when the animal opens 
ats valves}, it must receive, like the Mactre and Veneres, or any 
other bivalve with an open mantle, the currents of sea-water ; and 
an closing them, a great part thereof, after bathing the branchie, 
is ejected from the aperture of ingress, and only a portion of it 
passes out of the posterior orifices.” This I admit to be the 
natural effect of the opening and closing of the valves, but surely 
Mr. Clark does not mean to say that the branchial currents are 
produced by this means? According to my views this is an oc- 
casional action entirely independent of the regular branchial cur- 
rents, and should not be confounded with them, as these latter 
go on when the valves are entirely at rest, and when consequently 
no such effect as here described could possibly be produced by 
them. As to the siphonal fold being merely a prolongation of 
the mantle, this is the case with the siphons of all the Conchifera ; 
the only difference being, that in the present instance the tube 
is formed by a fold of the mantle, while in other genera, and in 
* See Lamarck, Anim. s. Vert. 2nd ed. vol. vi. p.7; Grant, Comp. Anat. 
p- 539; Owen, Lectures on Comp. Anat. vol. i. p. 282. 
¢ These words are here put in italics, though not soin Mr. Clark’s letter, 
to draw particular attention to them. I have taken the liberty of doing the 
same in other places. 
Ann. & Mag. N. Hist. Ser. 2. Vol. iv. 4 
