242 Mr. J. Alder on the Branchial Currents 



Nat. Hist. 1849, p. 339, pi. 13. f. 5, and which he also found 

 in the valves of Placuna sella. 



At the Scientific Congress held at Lucca (1843), Dr. Nardo 

 proposed a new classification of the Spongiadce, dividing them into 

 five families, under the names of Corneo-spongia, Silico-spongia, 

 Calci-spongia, Corneo-silici-spongia, Corneo-calci-spongia, these 

 famihes containing thirty genera*. 



XXVI. — On the Branchial Currents of the Bivalve Mollusca. 

 By Joshua Alder, Esq. 



To Richard Taylor, Esq. 



Dear Sir, Newcastle-upon-Tyne, 16th August 1849. 



It was not my intention again to have troubled you concerning 

 those points in the oeconomy of the Bivalves about which Mr. 

 Clark and I are at variance, but the concluding paragraph of that 

 gentleman's letter, in which he claims to have set at rest the use 

 of the anterior siphon in the genus Kellia, demands a few words 

 from me, lest my sileuce should be taken as an acquiescence in 

 such a statement. Perhaps I am also entitled to a reply to the 

 two new arguments by which my opinions are attempted to be 

 disproved. 



Mr. Clark has at length given us a distinct statement of his 

 views with respect to the admission of water into the branchial 

 cavity of the bivalves, which he attributes to the opening and 

 closing of the valves alone, and not to the action of cilia. Had 

 this been stated at first, some misunderstanding might have been 

 avoided. Undoubtedly a branchial current entering by a special 

 aperture, whether anterior or posterior, cannot be accounted for 

 by the opening and shutting of the valves. To explain such a 

 current the existence of ciliary action is required ; but I was un- 

 willing to believe that a gentleman of Mr. Clark's information 

 could entirely have discarded it. However, instead of arguing 

 this point further, I shall take the liberty of giving the result of 

 some observations made upon two or three species of bivalves 

 since the publication of my last letter. 



A small specimen of Modiola vulgaris, placed in a glass of 

 sea-water, gradually expanded the margin of the mantle beyond 

 the shell, and protruded the excretory siphon. When these were 



* Atti della quinta unione degli Scien. Ital. tenuta in Lucca, 1 843, p. 436. 

 The details of this paper have not I believe been published ; a short notice 

 however of the three first families appeared about fifteen years ago in Dr. 

 Oken's * Isis.' 



