1&6 Edible Mollusca of the Oregon Coast 
prospered in the Siuslaw River since its introduction about forty 
years ago, there are certain local conditions which may in time 
work toward its depletion. The North Fork, a tributary of the 
Siuslaw River of considerable size, pours its fresh waters, after 
a period of heavy rainfall, over the tide flats occupied by the 
clams. During times of unusually high water the tide flats are 
sometimes flooded continuously for several weeks at a time per- 
mitting much silt and sand to be deposited on the surface of the 
clam beds. During the latter part of December 1917 and through- 
out January, 1918, excessive rainfall caused exceedingly high 
water in both the Siuslaw River and its tributaries, as a result of 
which the clam beds were washed by comparatively fresh water 
for nearly four weeks. When examined at the end of January 
1918, a very high percentage of the young clams, then from 
20 to 30 mm. in length, were dead. They were alive and in good 
condition when examined in December 1917 just before the 
heavy rainfall. A dense layer of fine sand from % in. to 2 in. 
deep covered the surface of the clam beds after the recession of 
the high water, smothering, in my opinion, the younger and weaker 
individuals. Clams attaining a length of 50 mm. or more appar- 
ently were able to withstand these unusual conditions and sur- 
vived but practically all of the smaller individuals were destroyed. 
Beds of Mya arenaria of considerable size are found in the 
mud flats on the east side of Coos Bay opposite North Bend, 
from which source local markets are supplied. The species also 
inhabits certain tide flats of the Yaquina River above the town 
of Yaquina several miles from the ocean, and has gained a foot- 
hold in other bays and rivers along the northern half of the 
Oregon coast. 
5. Saxidomus giganteus Deshayes. 
Although this species has been taken at several points along 
the Oregon coast and its shells may be found scattered along the 
beaches, it has accumulated in but one locality in sufficient num- 
bers to be considered of economic importance. This clam is a 
characteristic one of Netarts Bay where formerly it was recog- 
nized as an abundant species (Figure I). During recent years, 
however, a gradual depletion of the species has been going on, 
[ 10 | 
