296 University of California Publications in Zoology [Vou. 23 
In addition to being found only on a rocky substratum, Hpialtus 
productus was always in patches of kelp, or in their immediate vicin- 
ity: at Point Bonita, Sausalito, and east of Fort Point. Spirontocaris 
taylori, another ‘‘hard bottom’’ species, was also taken only at locali- 
ties characterized by an abundant growth of algae along both shores 
of Golden Gate and in bunches of seaweed stripped from the piles 
of the Sausalito Ferry building. So far as our observations go, the 
only other middle bay species, excepting Spirontocaris paludicola men- 
tioned below, the distribution of which may be similarly conditioned, 
is Spirontocaris brevirostris, for although taken near the head of Rac- 
coon Strait on a bottom characterized simply as ‘‘stones,’’ it was also 
taken at the south side of Golden Gate in company with Spirontocaris 
taylorv. 
Though no doubt exercising a considerable influence on the 
distribution of the bay species, the effect of temperature and salinity 
on these bottom dwelling forms is much more difficult of demonstration 
and probably less important, at least within this section, than that 
exerted by the character of bottom. Of the species found exclusively 
in the bay only three were taken with the tow-net, Callianassa longi- 
mana, Cancer antennarius and Hemigrapsus oregonensis, respectively 
two, three, and one specimen each, the latter obviously an accident. 
Of the three middle bay species, Pandalus danae, Spirontocaris 
paludicola, and Pinnixa littoralis, not wholly restricted to the portion 
lying west of the line drawn above, the third was found only in the 
predominantly muddy eastern portion of the middle bay; the first, 
Pandalus danae, was returned but once from a ‘‘variegated mud 
...sand and fine gravel’’ bottom in this eastern portion, as com- 
pared with thirty-two specimens from a principally coarse sand gravel 
and stone bottom in the western portion of the middle bay; while 
the second, Spirontocaris paludicola, was taken but twice in the 
middle bay, once in its western portion, in the eel grass along the 
northern shore of Angel Island, and once in its eastern portion, from 
the algal growth in tide pools north of the Standard Oil pier, Rich- 
mond. 
b. In lacking a straining apparatus ‘‘for removing fine particles 
of foreign matter from its respiratory stream of water,’’ Cancer pro- 
ductus is ill adapted for life on more or less muddy or purely sand 
bottoms, and although recorded from the lower bay and the easterly 
sections of the middle bay, it was taken most frequently and abun- 
dantly in the western middle bay, as is to be expected. Here 
