D, Excurrent siphonal notch of the mantle margin.
The mouth is placed between the anterior adductor and the foot; the anus opens on a median papilla overlying the posterior adductor, and discharges into the superior pallial chamber along which the excurrent stream passes.
K, by the excurrent or superior siphonal notch of the mantle (fig.
It is through this passage, or indirectly through the pores of the gill-plates, that the water introduced into the lower subpallial space must pass on its way to the excurrent siphonal notch.
The atrial region extends from the mouth over about twothirds of the length of the body, terminating at a large median ventral aperture, the atriopore; this is the excurrent orifice for the respiratory current of water and also serves for the evacuation of the generative products.
Probe passed into the superior division of the subpallial chamber through the excurrent siphonal notch, and issuing by the side of the foot into the inferior division of the sub-pallial chamber.
A probe (g) is introduced through this slit-like passage, and it is seen to pass out by the excurrent siphonal notch.