242 Mr. J. Alder on the Branchial Currents 
Nat. Hist. 1849, p. 339. pl. 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 Spongiade, dividing them into 
five families, under the names of Corneo-spongia, Silico-spongia, 
Calci-spongia, Corneo-silici-spongia, Corneo-calci-spongia, these 
families containing thirty genera*. 
XXVI.—On the Branchial Currents of the Bivalve Mollusca. 
By Josuua Axper, Esq. 
To Richard Taylor, Esq. 
Dear Sir, Newcastle-upon-Tyne, 16th August 1849. 
Ir was not my intention again to have troubled you concerning 
those points in the ceconomy 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 Ked/ia, demands a few words 
from me, lest my silence 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 Lucea, 1843, 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.’ 
