PHOLAS. 193 
p- 370. pl. 15. N.S., on my branchial theory, which appeared 
in a paper on the Pholadide in vol. vi. p. 313 of that publi- 
cation. I was so engaged last year in the examination of a 
splendid harvest of rare animals, that I had no time to con- 
sider their remarks, but having now an unlimited supply of 
Pholades, 1 will endeavour to acquit myself of my engage- 
ments with these gentlemen. 
They commence by quoting parts of my theory, and say 
that I announce “ that 5% ths, if not all, the branchial water is 
admitted by the pedal gape.” On this pomt they observe— 
“ Let us for a moment consider what would be the conse- 
quence of Mr. Clark’s supposition, that these animals obtain 
water only by the pedal gape. Nearly all of them pass their 
lives buried in sand or mud, or immured in solid stone, with 
only a small aperture externally, the pedal opening being be- 
neath, and the siphonal tubes in communication with the sea. 
Yet Mr. Clark would have these animals receive only the 
small quantity of water charged with sand and mud that finds 
its way to the bottom of the cavity, rather than draw their 
supply from the pure element on the surface, by means of 
their long siphons.” 
To this quotation I reply, that a fresh and very extended 
examination of four species of the Pholades fully supports me 
in maintaining all my positions, and I think I shall demon- 
strate that Messrs. Alder and Hancock’s system of branchial 
currents is erroneous. The only correction I have to make 
is, that I have clearly ascertained that the branchial, like the 
anal siphon, is both inhalant and exhalant. 
With respect to their observations on the habits of the 
Pholades, it 1s only necessary to admit, that these animals 
often inhabit sand and shingle, mixed with clay, and are not 
always imbedded in hard rock. But we contend that the 
cavities mm which they dwell afford sufficient passage for the 
sea-water, and the areas of their habitats are saturated there- 
with, as when the tide withdraws, much of its waters is 
retained by the various strata, which by filtration reaches the 
burrows in a pure state, and not “charged with sand and 
mud.”? 
