Crenella T. Brown, 1827. Type species (M): C. elliptica T. Brown, 1827, Mytilus decussatus Montagu, 1808. Recent, North Atlantic. = Nuculocardia d'Orbigny, 1842. Type species (OD): N. divaricata d'Orbigny, 1842, Mytilus decussatus Montagu. Recent, Caribbean. Shell inequilateral, tumid, equivalve, small. Umbones not prominent, prosogyrate, with prodissoconch clearly demarcated. Periostracum thin, adherent. Sculpture of fine radial lirae, divaricating laterally, and some fine commarginal lirae, resulting in a decussate appearance. Hinge plate weak, with one or more small tubercles under beaks. Ligament opisthodetic, external, but sunken in a groove. Predominantly a cold-water genus that first appeared in the Cretaceous. The name is the Latin diminutive of crena, a notch; the gender is feminine.