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Cosa inornata (Hedley, 1904) (NEW COMBINATION)

Description: Shell minute, inflated. Prodissoconch semicircular, cup-shaped. Shape subovate, extended posteriorly. Anterior end concave dorsally, rounded ventrally; posterior end smoothly rounded. Umbones at anterior end of hinge. Hinge line straight, with microscopic denticles divided into 2 groups by wide triangular ligament pit. Interior white, margin crenulated; 4-6 broad, low ribs originate at posterior-dorsal margin. Exterior smooth apart from the 4-6 postero-dorsal ribs showing through, and on occasional specimens weak broad ribs towards ventral margin. Periostracum thin, fawn. Shell white.

Size: Up to 3.5 mm in length.

Distribution: Known from Cape Moreton, southern Qld southwards to Montague Island (off Narooma), NSW.

Habitat: Subtidal, 100-393 m depth.

Comparison: This species has the umbones at the end of the hinge as in C. pectinata, but differs by being almost completely smooth.

Fig.1: Top: 16 miles (26 km) east of Wollongong, NSW, in 183 m (PARATYPE, C.171630). Bottom: Off Sydney, 28 km east of Little Bay 183-192 m depth (C.364287)

Fig. 2: 16 miles (26 km) east of Wollongong, NSW, in 183 m (PARATYPE, C.171630)


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