Mr. W. Clark on the Animal of Kellia rubra. 455 
instead of being an open-mantled animal, is one of the closed 
‘mollusca,—where, in this case, is the entrance for the branchial 
currents? The only answer that can be given is, at the poste- 
rior branchial slit, and the discharge of the water must be at the 
same aperture. In this bivalve the feces are, as I have repeatedly 
seen, discharged from the rectum in minute pellets into the 
branchial slit, which in this animal undoubtedly performs three 
functions, those of ingress and egress of branchial currents, and 
a conduit for the feces. 
It may be asked, why has nature departed from her usual 
branchial scheme only in Kellia rubra and K. suborbicularis? We 
will now examine into the “cui bono” of this fold of the mantle, 
considered as a branchial appendage. It is well known that 
nature never acts by way of surplusage ; and having given Kellia 
rubra an open mantle by which the currents can enter, as in 
other analogous open bivalves, we must conclude she has not 
departed from her usual scheme, and that this fold is not a spe- 
cial branchial organ, but is intended to fulfill other functions. 
I will mention what perhaps may be considered a conclusive 
proof that the tube-like fold of the mantle cannot be intended 
_ for the ingress of branchial currents, which is, that the animal 
very often thrusts its foot into the fold, and by the with- 
drawal 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 
regular, delicate, and uninterrupted branchial currents ? 
May we not infer from this constant alliance of the foot with 
the fold, that there is a more intimate functional connexion be- 
tween them, perhaps of a locomotive nature ? 
_I will now very shortly state the grounds of my conjecture, 
that the fold in question is to aid the animal in locomotion. 
The habitat of this singular creature is at a far greater eleva- 
tion in the littoral zone than any other bivalve, and nearly as far 
removed from the level of the water as the Littorina petrea, which 
is at no time completely submerged im the sea. The Kellia rubra 
on the Devon coast near Exmouth is generally imbedded in the 
Lichina pygmea, which grows in the cavities of rocks of such 
considerable elevation and so near the land, that thousands of 
these animals pass their entire existence without perhaps ever 
being completely in a condition to receive branchial currents of 
sea-water ; even the spray rarely reaches them except in gales of 
wind. It appears then that the tides washing the bases of their 
rocky habitat, combined with the saline mixture of atmospheric 
particles, supply a sufficient humidity for the growth of the Li- 
china pygmea and the sustentation and welfare of the bivalve 
