144 Mr. W. Clark on the Animal of Kellia rubra. 



having separate apertures, as an acquittance on account of those 

 parts of his observations which I have neglected to notice, and 

 which, if established, will I am sure be considered by that gen- 

 tleman as a sufficient answer. 



I propose to demonstrate that the water for branchial, as well 

 as alimentary purposes, passes into the branchial cavity by both 

 the posterior siphons, in conjunction with the pedal aperture in 

 those animals in which the ventral range is sufficiently open, and 

 is expelled indiscriminately in various proportions from all the 

 apertures T have mentioned. 



It appears entirely to have escaped Mr. Alder^s observation that 

 the posterior siphons of all bivalves have other functions besides 

 the conveyance of water to the branchiae, and that they are also 

 furnished with most important organs of prehension, for pro- 

 viding for the animaFs sustentation ; these are the tentacular 

 cirrhi and cilia which clothe both the anal and branchial siphons 

 of a great majority of the bivalve mollusca, to entangle and cap- 

 ture the minute animalculse to be conveyed into the branchial 

 cavity : how, and by what means, is this operation to be accom- 

 plished ? I answer, through both the posterior ciliated siphons, 

 by the agency of the currents of water, which enter and thus 

 enable them to deposit within the branchial walls the prey which 

 each cirrhigerous siphon has captured. We cannot suppose that 

 nature has furnished the siphons of the animals with organs for 

 taking their prey, without at the same time providing the means 

 of conveying it into the branchial cavity, and there cannot be 

 any other than the passage of the water through each siphon. 

 We have here irrefragable proof that both the posterior siphons 

 are subservient to provide the animal with water for branchial 

 and alimentary uses. 



The Pectines, Anomm, and Ostrece also indisputably prove the 

 fallacy of Mr. Alder's doctrine of distinct apertures of ingress 

 and egress for the branchial currents, as in these genera the 

 animals have only one immense aperture, which extends nearly 

 throughout the periphery of the shell, consequently the water 

 can only enter into and issue from the same aperture. . 



The only other point I must notice is Mr. Alder's assertion 

 that I have " overstated " the tidal range oi Kellia rubra. What 

 I said with respect to the habitat of this species, was from the 

 recollections of fifteen years ago. I visited the locality a few 

 days since, and again this day, with a person well acquainted 

 with the coast, who called in to assist his judgement another in- 

 dividual, who informed me that the rock from which I took in 

 their presence Kellia rubra, is often not covered with water for a 

 fortnight at a time in calm weather : therefore, as I stated in my 

 last paper, the washing of the bases and sides of the rocks suffices 



