1914] Sumner, et al.: Physical Conditions in San Francisco Bay o 
thus far has been the breaking of some of the teeth. Since these are 
fastened to the frame by bolts, they may readily be replaced. 
(5) An iron mud dredge, of the type known commercially as the 
‘‘orange-peel bucket’? (pl. 10). The one employed was the ‘* Dwarf 
Bucket, No. 7’’ of the catalogue of the Hayward Company of New 
York. The capacity, according to the manufacturer’s statement, was 
21% eubie feet (0.07 eubie meter). Since, however, in our work the 
mass of mud commonly projected from several inches to a foot above 
the rim of the bucket, it is probable that we sometimes obtained twice 
the volume stated. As employed by us, this mud bucket was operated 
by a single cable, the closure being effected by means of an automatic 
tripping mechanism devised for the purpose. For ordinary indus- 
trial uses two cables are employed with this apparatus, one of which 
is used for lowering it, the other for closing and raising it. In our 
device the fall of a ring, following the grounding of the dredge, 
released the cable from its connection with a hook (‘‘slip-hook’’) fas- 
tened to the upper end of the apparatus. As soon as the reeling in 
was commenced the strain was transferred to a terminal section of 
extra flexible cable, wound around a sheave, the revolution of which 
brought together the blades (pl. 10, figs. 11-13). 
A conical canvas hood was adjusted to the upper frame of this 
dredge, in order to prevent the washing out of the contents while 
being raised through the water. During descent a large flap, or valve, 
permitted the water to escape. 
So far as we know, ours is the first application to biological ex- 
ploration of this type of apparatus. After considerable experience, 
we can unreservedly recommend its use for such purposes, at least 
in relatively shallow waters. Its chief advantage lies in the taking 
of comparatively large masses of mud from a single spot, and partic- 
ularly in the penetrating power of the apparatus which renders pos- 
sible the capture of deeply burrowing annelids, lamellibranchs, ete. 
The material brought in by these various types of dredges and 
trawls was emptied upon a graduated series of screens (the ‘‘table 
sieve’’ of Verrill and Chester) and subjected to washing with a hose. 
The coarsest of these screens had meshes one inch square, the finest 
having meshes one twenty-fourth inch square. The organisms of 
various groups were sorted and preserved, either on deck or in the 
laboratory, and were subsequently referred to specialists for exam- 
ination. 
In the plankton collecting, three tow-nets were used simultaneously, 
these being operated on the dredging cable. A large net of 000 silk 
