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 rahra : 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 cu'culation, 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 branchiae within the 

 fissure, which he seems to consider a proof of its being a branchial 

 (ingress ?) aperture. The branchiae 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 sub orbicularis 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 

 E. Forbes has suggested that the open or close form of the tube 



Ann, ^ Mag. N. Hist. Ser. 2. Vol. iii. 25 



