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PHOLADIDAE 461
the valves. No scientific study has been made of this variant, but it may be
due to environmental or dietetic conditions.
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Figure 94. Mud, peat and rock borers of the Atlantic Coast, a, Angel Wing,
Barnea costata Linne; b, Petricola pholadifonnis Lamarck, False Angel Wing
(p. 420); c, Northern Piddock, Zirfaea crispata Linne. All slightly reduced.
(From Gould and Binney 1870.)
Barnea truncata Say Fallen Angel Wing
Massachusetts Bay to south Florida.
2 to 2/4 inches in length, somewhat resembling the Angel Wing, B.
costata, but widely gaping at both ends, truncate at the posterior end,
smoothish at the posterior half, and with an elongate, narrow accessory
plate over the beak area. Shell fragile, white to grayish white. The internal
condyle is long and about the thickness of a toothpick. The siphons are
encased in a large, rough, gray, tubular sheath which may be extended 2 to
3 times the length of the shell. Bores into clay, soft rock or wood. Common
in intertidal zones. Do not confuse with Zirfaea crispata which is much
more squat and has a radial, indented line dividing each valve into 2 areas.
Barnea siibtnmcata Sowcrby 1834 Pacific Mud Piddock
San Francisco, California, to Lower California.