Mr. J. Alder on the Animal of Kellia rubra. 385 
in one direction, and the passing in of one portion of water is 
consequent on the displacement and passing onwards of another 
portion, so that both processes are going forward at the same 
time. The two apertures are always present in those genera 
where the mantle is more or less closed, though one of them is 
- sometimes confluent with the pedal opening. ‘They are usually 
siphonal, and have been called the branchial and anal siphons ; a 
mode of appellation not altogether correct, as both are alike sub- 
servient to branchial and alimentary purposes ; the one (inhalant) 
being branchial and buccal; the other (exhalant) branchial and 
anal. In the former the current is pretty regularly sustained ; 
in the latter the water is usually expelled by an intermittent mo- 
tion and occasionally by jerks. I should not have thought it 
necessary to be thus minute in detail did not Mr. Clark’s argu- 
ments lead to the supposition that he takes the words branchial 
and anal, as applied to these apertures, in a literal and restricted 
sense, which they are not intended to bear. But to return to 
Kellia rabra : the contraction and expansion of the posterior ori- 
fice is no more than is seen in the excretory siphon of all bivalves, 
and has no power to produce the internal circulation, but merely 
to regulate the discharge, and in this case, where the orifice is a 
mere slit, the ejecting force is very limited. The situation of the 
anus, as pointed out by Mr. Clark, is no doubt correct, and in 
the usual place opening behind and within the egress-aperture. 
Mr. Clark, however, saw the points of the branchie within the 
fissure, which he seems to consider a proof of its being a branchial 
(ingress ?) aperture. The branchie of this species are of a tri- 
angular form and very unequal in size, the lower angle extending 
down posteriorly very near to the orifice, but it does not enter it, 
and I think no conclusion can be drawn from this circumstance ; 
at least, none that can be set against the evidence derived from 
the actual sight of the currents, which any one may obtain, espe- 
cially the inhalant one, in the way that I have pointed out. 
The superior size of Kellia suborbicularis renders it less liable 
to be misunderstood. Having frequently had this species alive 
for several days together, both before and after ascertaining the 
peculiarities of Kellia rubra, 1 am sufficiently familiar with it to 
speak confidently concerning its anterior siphon, which, as I have 
more than once stated elsewhere, is a perfect tube, closed below, 
through which the branchial current may be seen to enter. This 
is perhaps the only described species in which the tube is really 
perfect, for M. Deshayes was most likely deceived with respect to 
the Mediterranean Kellia rubra (Bornia siminulum) in the same 
manner that Mr. Clark and I had been on a first examination. 
To reconcile the conflicting statements of authors, Professor 
EK. Forbes has suggested that the open or close form of the tube 
Ann. & Mag. N. Hist. Ser. 2. Vol. iii. 29 
