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PHOLADIDAE 463
which is supported by about a dozen, vertical, shelly plates. Not very common.
Genus Xylophaga Turton 1822
Xylophaga ivashingtona Bartsch Washington Wood-eater
Washington and Oregon.
% inch in length, globular and fragile. The large anterior gape has %
of its area covered by a triangular callum in each upper and outer corner.
Middle of inside of each valve reinforced by a small, strong, radial cord vi^hich
is welded to the valve. Color yellowish white. Bores into pieces of water-
logged wood. Uncommonly collected in dredging hauls.
The Atlantic species X. dorsalis Turton has much the same characters
as the above species. It occurs from loo to 300 fathoms from the Arctic
Seas to off Cape Cod.
Genus Fenitella Valenciennes 1846
PeJiitella penita Conrad Flap-tipped Piddock
Bering Sea to San Diego, California.
1 % to 3 inches in length, elongate to moderately short, rotund anteriorly,
becoming compressed and narrow posteriorly where there is a leathery pro-
longation protecting the siphons. Anterior gape commonly closed by an
eggshell-like, globose, callus plate which continues up on to the beak region
in the form of a pair of rather large plates. Just in back of these there is a
short, triangular plate or protoplax set on top of the middle of the dorsal
region. Otherwise somewhat resembling the large Farapholas californica.
Commonly found boring in rocks and shale. The form sagitta "Stearns"
Dall lacks the calcareous covering over the foot gape. It is found with the
typical form.
Genus Fholadidea Turton 18 19
Pholadidea ovoidea Gould Wart-necked Piddock
Bering^ Sea to the Gulf of California.
2 to 3 inches in length, very similar to pilsbryi, but oval in side view.
About half of the anterior foot gape is covered by eggshell-like, smoothish
calcareous material. It is not impossible that pilsbryi is an ecological form
of this species. More studies in their natural history are needed. Moderately