OYSTER RESOURCES OF THE PACIFIC COAST. 349 
fish. Its presence requires the fencing in of all the oyster beds in the 
bay with closely set stakes about 12 feet long, which are driven about 4 
feet into the ground. Plates 8 and 9 show the nature of these fences. 
When a broken stake allows a school of stingrays to raid an oyster bed, 
the surface, after the tide has gone out, presents much the appearance 
of a field that has been rooted by hogs. Sometimes. the oystermen, 
discovering their presence, manage to entrap them inside the line of 
stakes, and thus destroy many of them during one low tide. | 
Fencing oyster beds against stingrays constitutes another heavy 
expense to the California oystermen, in addition to the annual outlay 
for seed oysters from the Atlantic coast. The fences must be looked 
after constantly and kept in repair. The heavy winds that sometimes 
during the winter season cause vessels in San Francisco Bay to drag 
their anchors do great damage to the fences of the oystermen, which 
they must manage to have in good condition by the time the stingrays 
reappear in the bay. 
I do not know how late in the fall stingrays continue to menace the 
oysters, but I netted a few small specimens in San Pablo Bay as late 
as November 7, 1890. They first appear in April. 
The danger from stingrays is probably overestimated, in view of 
the natural increase of oysters upon wide tracts unprotected by stakes. 
Other enemies of the oyster.—The drill (Urosalpinx cinerea) has not 
become troublesome upon the oyster beds of San Francisco Bay until 
very recently, and even now is abundant only in the southern part of 
the bay. The oystermen showed me heaps of shells, all more or less 
drilled with small holes, in evidence of its ravages. At the Belmont 
beds I had no difficulty in gathering a quart of these mollusks in less 
than ten minutes by merely turning over the large oysters when the 
water had receded from the beds. Sometimes half a dozen were to be 
found on a single oyster. With its minute ‘“tongue-file” this creature 
drills a hole through the oyster’s shell, and inserting its proboscis into 
the opening, barely large enough to admit a pin, it feeds directly upon 
the soft parts. 
This destructive animal may have been introduced much earlier than 
the oystermen suppose, as a few individuals accidentally imported 
among the original oysters would require several years to increase to 
the present numbers. Mr. Moraghan informed me that there were no 
drills upon his beds at Millbr ae, which, as stated above, are much nearer 
the sea than the Belmont beds. If they are restricted to the Bel- 
mont beds, as seems to be the case, it would pay the oyster-growers to 
pick them off as far as possible. Any gathering of drills that would 
_ keep them in check is important, as their increase will cause great loss 
in the future. 
Two species of crabs are found upon the San Francisco oyster beds, 
one of which is exceedingly abundant, but their presence has probably 
no effect upon the oysters. 
