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Rh valves). Concentric ribs fairly even, well-developed, numerous. Periostra- cum light- to dark-brown. Commonly found in mud just below low-tide mark.

Figure 71. Nut and Yoldia Clams, a, Nuculana teimisiilcata Couthouy, % inch (Atlantic); b, Yoldia liinatiila Say, 2 inches (Arctic waters, both coasts); c, Yoldia montereyensis DzW, i inch (California). Nuculana carpenteri Dall North Carolina to West Indies. Carpenter's Nut Clam About Vi inch in length, compressed, thin, translucent yellow-brown, with a long, slightly upturning rostrum. Anterior end round. Umbones very small, close together. Almost smooth except for minute, concentric growth lines and microscopic axial scratches which are absent in dead, white valves. Commonly dredged offshore from 10 to 100 or more fathoms. Nuculana fossa Baird Fossa Nut Clam Alaska to Puget Sound, Washington. % to I inch in length, elongate, moderately fat and smoothish except for small, pronounced, concentric ribs at the anterior end and on the beaks. Dorsal area of rostrum smoothish, depressed and bounded by 2 weak radial ribs. Periostracum dark- to light-brown. Dredged offshore in shallow water. Some workers consider the following forms or variations as subspecies: sculpta Dall, vaginata Dall and curtulosa Dall. Subgenus Ledella Verrill and Bush 1897 Nuculana ?nessanensis Seguenza Messanean Nut Clam Cape Cod to the West Indies.