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THYASIRIDAE |
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Genaxinus albigena (Hedley, 1907) Description: Shell very small, well inflated, translucent. Shape almost circular, slightly higher than wide; umbo on midline; lunule large, shallow. Exterior with weak, irregular, concentric growth ridges, no radial sculpture. Interior with anterior and posterior muscle scars elongate, greatly thickened, opaque, raised above shell surface. Pallial line not observed. Margin smooth. Hinge not observed. Ligament in long, narrow groove. Shell colour white. Size: Up to 2.2 mm in height. Distribution: Known only from two lots from off Sydney. Habitat: Type lot from 800 fathoms (1463 m) 36 miles (58 km) east of Sydney. Another lot in 750 m, off Sydney. Comparison: This species stands out because of the unusual thickening of the muscle scars, forming raised, opaque, teardrop-shaped pads in the interior of the shell. This character has not been noted in any other NSW bivalve. Fig. 1: Off Sydney, in 750 m (C.445226). Left valve broken on posterior side. |
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