Page:American Seashells (1954).djvu/422

340 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 Figure 71b Maine to Cape May, New Jersey. Northern Alaska. 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 Plate 27b Arctic Seas to North Carolina. % 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.