648 JAMES L. KELLOGG 
considerable distance from the palps, the distal oral groove (dg) 
being long in consequence. 
Mantle. The mantle ciliation apparently does not, as in 
Mactra, possess the single, posteriorly directed, cilia tract. 
There is a short waste canal (wc) into the anterior end of which, 
in the usual manner, mantle collections are led. As in other 
forms possessing a waste canal, a well developed siphon mem- 
brane is present. 
Spisula planulata Conrad 
This Spisula was studied at San Diego Bay, California. 
Gills and palps. The ciliation of these organs is like that of 
the form just mentioned. 
Mantle. There is the single line extending backward to the 
bay at the base of the incurrent siphon (fig. 11, 6). Waste canal 
and siphon membrane, however, are absent. There thus seems 
to be considerable difference in the ventral region of the mantle 
in these two species of Spisula. 
Sazxidomus gigantius Deshayes 
Gills. Streams on all lamellae are to the margins, in this 
Puget Sound form. 
Palps. The attachment of posterior palps to the wall of the 
visceral mass is not extensive. The ciliation of both faces is 
practically the same as in Schizotherus. 
Mantle. The edges are not fused; the siphon tubes are rela- 
tively large; the mantle edge possesses a very wide thickening. 
As in Venus, there is a sharply defined curved line in the general 
ciliation of the mantle wall (fig. 12, m), extending from the 
anterior adductor to the bay below the incurrent siphon (6), 
where mantle collections lodge before being ejected through the 
siphon tube. At the base of the incurrent siphon, is a siphon 
membrane (sm) of unusual construction, a circular structure 
with a central aperture, which is opened wide with a circular 
outline, or nearly closed into a vertical slit. This structure 
probably cannot throw the entering stream downward, and there 
