Oval, inflated, umbones central to slightly anterior, thin-walled, white or tan to yellowish gray, with numerous fine, divaricating radial ribs; interior glossy white and faintly iridescent, margin finely denticulate, hinge finely dentate, dorsal hinge margin finely vertically striate. Arctic circum-boreal, eastern Canada to Florida, Bahamas, West Indies, Gulf of Mexico, Caribbean Central America, South America (to Argentina). Length 2 mm (to 6 mm). Syn. divaricata d'Orbigny, 1853. Note: Also known as Decussate Crenella.

CROSS-SCULPTURE CRENELLA Mytilus decussatus Montagu. 1808: 69; Crenella elliptica T. Brown, 1827: pl. 31; Nuculocardia divaricata d'Orbigny, 1842: pl. 27; Modiola? cicercula Möller, 1842: 92; Crenella? inflata Carpenter, 1864b: 313: C. divaricata Yokoyama, 1922: 175, non (d'Orbigny, 1842); C. yokoyamai Nomura, 1932: 74, nom. nov. pro C. divaricata Yokoyama, non (d'Orbigny); C. ecuadoriana Pilsbry and Olsson, 1941: 55; C. decussata laticostata Scarlato, 1960: 65. Shell ovate, inflated, with conspicuous radial riblets, which may bifurcate ven- trally. Length to 10 mm. Attempts to recognize two taxa here, a northern, coarsely sculptured species and a southern species with finer, more bifurcating ribs, quickly fall apart. This species- complex would prove an interesting topic for more detailed study. The relationships of this species to C. nomeana MacNeil, in MacNeil et al. (1943), from the Pliocene of Alaska, and to C. ecuadoriana santiaga Olsson, 1964, from the Miocene of Ecuador, merit investigation. Arctic and circumboreal. Beaufort Sea, Alaska (71°N) [LACM], south through the Golfo de California and to northern Perú (3.5°S) (Olsson, 1961), and the Islas Galápagos (1.0°S) [LACM]; in Atlantic from North Carolina to the Caribbean and south to the British Isles; south to Japan in northwestern Pacific; in the intertidal zone to 200 m. Recorded as early as the Pliocene in western North America. Literature: F. R. Bernard (1979b: 24), U. S. Grant and Gale (1931: 254), Hertlein and Grant (1972: 171), Hertlein and Strong (1946a: 75-76), Keen (1971: 65), Lubinsky (1980: 24), E. J. Moore (1983: 71-72), Ockelmann (1959: 51-52), Olsson (1961: 130), Poppe and Goto (1993: 48), Scarlato (1960: 63-65, 1981: 220-222), Soot-Ryen (1955: 80-81), Theroux and Wigley (1983: 15-16), Valentich Scott (1998: 122-123).

Crenella decussata (Montagu, 1808) Cross-sculpture Crenella Distribution: North Carolina to Florida, Texas; West Indies; U.S. Pacific coast. Size: 3 mm (½ in). Description: Color white to yellowish, interior glossy white; shape subcir- cular; sculpture with dominant radial ribs and more numerous concentric riblets between radials that slightly overlap, appearing finely cancellate; larger commarginal growth lines prominent toward ventral margin; beak slightly rolled inward; hinge teeth with 3 cardinals, interior ligamental shelf on inner postero-dorsal margin leading to erect lateral teeth. Habitat: Calcareous and mud bottoms. In Texas found at FGB. Depth range 0 to 250 m (820 ft). Remarks: C. divaricata Yokoyama, 1922 was a subspecies of C. decus- sata; however, Coan and Scott (1997) concluded that C. divaricata is a synonym of C. decussata. See Tunnell et al. (1978); Coan et al. (2000); Mikkelsen and Bieler (2004). Synonym: C. divaricata Yokoyama, 1922.