18 University of California Publications in Zoology [ Vor. 14 
When the apparatus is to be used, the upper rod or stem is pushed 
down. The lugs are rotated inward (against the force of spiral springs 
in their interior), so that they come to lie above the transverse bar 
and block its ascent to the upper limit of the stirrup. When lifted 
by the ring or eye at the top, the weight of the apparatus is thus 
thrown upon the stirrup, but no pull is exerted upon the slender rod 
controlling the lower valve. 
In our work, the apparatus is dropped freely from a distance of 
some feet above the water line, the rope being allowed to run out with- 
out hindrance. Upon reaching the bottom the upper sliding rod falls 
of its own weight, carrying with it the transverse bar and releasing 
the lugs, which assume their original positions. When the line is 
reeled in this rod and bar are now free to slide upward as far as the 
stirrup will allow. In so doing the slender rod is drawn up, thus 
closing the lower valve. This slender rod is made in two pieces, which 
are connected by a temporary link of copper wire (pl. 12, fig. 15) just 
below the flanges. The object of the latter arrangement is to save 
the valve from damage, in ease it is prevented from closing by the 
presence of a stone or large shell. In that ease the whole weight of 
the instrument (plus the force required to extricate it from the mud) 
is thrown upon the wire link, which breaks and relieves the valve of 
further strain. Ordinarily, one thickness of no. 14 (American gauge) 
copper wire has been used for making this link. 
The upper valve allows the water to escape from the tube during 
the descent of the apparatus, while preventing its entrance during 
ascent. The lower valve prevents the escape of the mud during the 
ascent, though it has sometimes failed to close completely when the 
wire link was too long. Its complete closure is not, however, necessary 
in tenacious mud, provided that the upper valve functions properly. 
This apparatus cannot be used except upon bottoms of mud or of 
fine sand. The cutting edge at the lower edge is naturally blunted 
and dented by striking stones, and for this reason extra parts are 
necessary. Shells, however, are frequently found to be cut rather 
smoothly, even the comparatively thick shell of the native oyster 
(Ostrea lurida) having, on oceasions, been stamped out as if by a 
punch. In general, the depth to which the tube penetrates is inversely 
proportional to amount of sand, shells or other matter contained in 
the mud. In perfectly clear mud, such as that found near the southern 
end of San Francisco Bay, perfect samples 180 em. in length (1.e., up 
to the capacity of the apparatus) were taken on a number of occasions. 
