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340 American Seashells
Genus Yoldia MoUer 1842
Somewhat similar to Nuculana, but the valves are much thinner and
fragile, rarely with a long rostrum, usually gaping at both ends, much
smoother and glistening.
Subgenus Yoldia s. str.
Yoldia limatula Say File Yoldia
Maine to Cape May, New Jersey. Northern Alaska.
Figure 71b
I to 2 ^ inches in length, elongate, narrowing at the posterior end. Um-
bones very small, halfway between the ends of the shell. Exterior glistening
greenish tan to light chestnut-brown, with only faint concentric growth
lines. Interior glossy white. A rather common species just below low-water
mark. Distinguished from Y. sapotilla by its more elongate shape. It is pres-
ent in northern Alaska, but it is replaced to the south by the following sub-
species.
Yoldia limatida gardneri Oldroyd Gardner's Yoldia
Southern Alaska to off San Diego, California.
Very similar to the true Innatida, but always having the anterior ventral
margin with a small concave depression. In general shape it falls within the
variations of the Atlantic specimens. Moderately common.
Yoldia sapotilla Gould Short Yoldia
Arctic Seas to North Carolina.
Plate 27b
% to 1% inches in length, oblong, smooth, with a moderately extended
posterior end. Periostracum yellowish to greenish brown. Differing from
limatula in being shorter and less extended and more truncate at the poste-
rior end. Commonly dredged off New England in shallow water; often
found in fish stomachs. This species can be confused with the uncommon
Y. myalis Couthouy (pi. 2 yd) which is found from Labrador to Cape Cod
and Alaska and which, however, is shorter and more pointed at the posterior
end.
Subgenus Megayoldia Verrill and Bush 1897
Yoldia thraciaejormis Storer Broad Yoldia
Plate 276
Arctic Seas to Cape Hatteras, North Carolina. Alaska to Puget Sound.