Diagnostic characters: Shell equivalve, laterally compressed to subcylindrical in cross-section, with
a narrowly elongate, often sword-like or razor-like shape, very inequilateral and gaping at both ends.
Umbones not prominent, frequently near the anterior end of dorsal margin. Outside of shell essentially
with concentric growth marks, often changing abruptly in direction along a diagonal line running from the
umbones to the posteroventral end of valves. Periostracum prominent, frequently glossy. Ligament
external, set in an elongate linear groove of posterodorsal margin. Hinge feeble, with at least 1 peg-like
cardinal tooth in each valve, and sometimes 1 or 2 lamellar posterior teeth. Interior of shell porcelaneous.
Two dorsally placed, narrowly elongate to rounded, adductor muscle scars, the anterior one commonly
larger. Pallial sinus relatively shallow, its ventral, and even sometimes dorsal limb largely confluent with
pallial line. Internal margins smooth. Gills of eulamellibranchiate type, posteriorly placed, with smooth or
folded branchial sheets.Foot long and narrow, often terminally swollen.Siphons naked, short to long, fused,
at least at their base. Mantle margins widely fused ventrally, with an anterior to anteroventral opening
Diagnostic characters: Shell equivalve, laterally compressed to subcylindrical in cross-section, witha narrowly elongate, often sword-like or razor-like shape, very inequilateral and gaping at both ends.Umbones not prominent, frequently near the anterior end of dorsal margin. Outside of shell essentiallywith concentric growth marks, often changing abruptly in direction along a diagonal line running from theumbones to the posteroventral end of valves. Periostracum prominent, frequently glossy. Ligamentexternal, set in an elongate linear groove of posterodorsal margin. Hinge feeble, with at least 1 peg-likecardinal tooth in each valve, and sometimes 1 or 2 lamellar posterior teeth. Interior of shell porcelaneous.Two dorsally placed, narrowly elongate to rounded, adductor muscle scars, the anterior one commonlylarger. Pallial sinus relatively shallow, its ventral, and even sometimes dorsal limb largely confluent withpallial line. Internal margins smooth. Gills of eulamellibranchiate type, posteriorly placed, with smooth orfolded branchial sheets.Foot long and narrow, often terminally swollen.Siphons naked, short to long, fused,at least at their base. Mantle margins widely fused ventrally, with an anterior to anteroventral opening
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