Mr. J. Alder on the Animal of Kellia rubra. 53 
that she has not departed from her usual scheme, and that this 
fold is not a special branchial organ, but is intended to fulfill 
other functions.” Is this a legitimate conclusion to arrive at ? 
Mr. Clark here argues as if the departure from the usual scheme 
in Kellia rubra was in having a special branchial orifice ; but this 
is not the point of difference, as I have before stated, and these 
objections, if they have any weight, must apply equally to the 
posterior branchial siphons of all the open-mantled bivalves. 
They all have a pedal aperture through which the currents can 
enter. What then is the use of the so-called branchial siphon ? 
Or why are there three apertures performing the same function ? 
Surely there is something very like surplusage here. The “ cuz 
bono” may well be asked of Mr. Clark’s views, but not of mine, 
as I assign a separate function to each orifice: the branchial one 
being kept apart from the opening for the foot in order that the 
currents may not be interrupted by the action of that member. 
But Mr. Clark says, the foot does intrude itself occasionally 
into the folded siphon of Kellia rubra; and this is the last and 
“conclusive proof” by which I am to be put hors de combat. 
“The animal very often thrusts its foot into the fold, and by the 
withdrawal of which it is opened and the edges separated. How 
then can a fold, whose form by this action is continually changing, 
and is subject to momentary interruption, be the conduit of re- 
gular, delicate, and uninterrupted currents ?” I would ask, does 
not this objection tell more strongly against the true pedal 
opening of this and other bivalves, which Mr. Clark wishes to 
make out is the principal one for the entrance and exit of 
branchial currents? Let any one look at this little animal with 
its siphonal fold stretched out in front, and frequently expanded 
almost into a cup-form, as if courting the entrance of the vivifying 
stream, and then say whether the basal part through which the 
foot is constantly protruded when in action, or the siphonal fold 
into which it not unfrequently makes a momentary incursion, 1s 
most free to supply the currents necessary for respiration and 
food. Mr. Clark calls these currents “regular, delicate, and un- 
interrupted.” I have said that they are continuous, and pretty 
regularly sustained, but never contemplated asserting that they 
were not liable to occasional or accidental interruption. 
I shall now briefly advert to the curious use which Mr. Clark 
has found for the siphonal fold as a prehensile organ, and the 
no less curious terrestrial habits which he supposes this little 
bivalve to possess. For both I think that gentleman is greatly 
indebted to a lively imagination. Probably he will also find, 
ona more careful examination, that its habitat beyond tidal range 
has been rather overstated. I have never found it but withm 
tide-marks, and cannot conceive how a bivalve mollusk, whose 
