684. JAMES L. KELLOGG 
Excepting this organ, the ciliation of the body conforms, in 
general, to that usually found in bivalves. 
Proceeding at once to a description of what may be called for 
lack of a better name, the collecting membrane of the visceral 
mass, it will be noticed that the thin, filmy structure (fig. 57, cm) 
is an outgrowth of the posterior wall of the body (vwms), and 
projects into the mantle chamber. It may be retracted close 
to its base, or extended backward for a great distance, when 
fully performing its functions being thrust into the incurrent 
siphon tube. Because of its great power of extension, it does 
not seem impossible that its end may sometimes be projected 
entirely through the siphon tube. It tapers from base to tip, 
and has the form of an inverted trough. In the figure, cilia 
currents on the extensive collecting area of the visceral mass, 
below the line of gill attachment (ga), converge on each side of 
the body to the base of the membrane, on its ventral edges, 
at the points x, right and left. An attempt has also been made 
to show that the outer or upper convex surface of the membrane 
is ciliated, and carries material to the same regions. Here all 
collections pass to the under, concave, surface of the collecting 
membrane, and are carried swiftly backward, directly in the 
face of the incoming stream of water, to the tip of the membrane, 
as represented by dotted arrows. Here they are held—the tip 
usually resting on the siphon wall—until a ball of considerable 
size has been collected. This, and the mantle collection at b 
are discharged on contraction of the adductor muscles. 
Specimens in which this membrane was found, were taken 
from waters which frequently were almost thick with silt for many 
hours at a time, but it was observed that mud was never so 
abundant as to cause the creatures to withdraw their siphons, 
and so prevent its entrance to the mantle chamber. This was 
clearly seen at a stage of the ebb tide when only a film of water 
covered the flats in which individuals were numerous. The 
presumption is that, under such conditions, the ordinary means 
of removing mud were insufficient, and that this collecting 
membrane was developed as an aid. At any rate, that mud 
