1921] Schmitt: The Marine Decapod Crustacea of California 231 
bottom; where buoyed up by the water they move lightly over the ground on the 
tips of their legs, presenting a striking contrast to their heavy and clumsy move- 
ments as ordinarily seen on land. If frightened they dart away with surprising 
speed. Some of the fish eaten by them must require much agility in their cap- 
ture, though how this is accomplished is unknown. For the greater part of the 
time, however, they lie almost entirely buried in the sand, as may be seen from 
observation in the aquarium or in shallow bays. If examined at such a time, 
only the stalked eyes, antennules, and antennae will be visible, and below these 
a sort of chink between the anterior part of the shell and the flattened maxillipeds 
which are held slightly separated from the body. From this cleft issues a current, 
evident if the water is roily, or in the laboratory if India ink, for instance, be 
added. 
When thus buried two conditions must be met: First and most important, a 
supply of fresh water for respiration must be obtained; and, second, the animal 
must be informed of the presence of food or enemies. Under ordinary conditions 
the water is forced through the gill-cavity by the rhythmic beating of a specialized 
appendage lying in an anterior prolongation of the chamber; the water is drawn 
in near the bases of the legs and escapes near the mouth, forming the exhalent 
current already noted. When buried, the water must be drawn from the surround- 
ing sand, but it must also be freed from fine sediment which soon coats the plates 
of the gills and interferes with respiration. If India ink be discharged on the 
surface of the sand above a buried crab, it will be drawn into the sand along two 
lines corresponding to the front borders of the shell, and closer observation will 
show that it passes into a crevice between the shell and the large pincers, which, 
when folded, accurately fit the contour of the sides of the body, here covered with 
a dense plush-like coat of hair. The teeth on the overhanging edge of the shell 
exclude large grains of sand, while the hair acts as a very efficient strainer, 
removing all fine particles from the inhalent stream. At times the direction of 
this current is reversed. 
These facts explain certain of the habits. Other forms, though closely related, 
may lack this straining apparatus and thus be unable to burrow in sand; this 
is the case with Cancer productus, which, as a result, is restricted to rocky or 
gravelly bottoms. In the edible crab this straining apparatus, though efficient 
in removing the sediment found in the sand, seems less satisfactory in dealing 
with the finer particles of muddy bottoms, and crabs found in these locations 
have the gills badly discoloured and seldom appear healthy. Other questions, such 
as food and the adaptation of the legs to sand-burrowing, may have some influence, 
but the preference for sand is largely due to the method of respiration. 
The bay specimens of this species, like those of C. productus and 
C. antennarius, are for the greater part much undersized. Of the 
total three hundred and eleven specimens taken, very few, only one 
or two, were really of notable size; a great number were at best of 
medium size, and a still greater number were small or juvenile ; ninety- 
six measured specimens averaged only 31.6 mm. in width. This is 
quite in keeping with Weymouth’s observations (1914, p. 124) regard- 
ing the reduction in size of this species as a result of over fishing: 
The following quotation pictures the condition about 1880: ‘‘The common 
crabs are caught along the sandy beaches on the San Francisco side of the bay, 
especially on the south side of the Golden Gate between the city and the sea. They 
