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Semicassis thomsoni (Brazier, 1875)

Description: Whorls angulate, spirally ribbed and striate. Body whorl with a broad, shallow spiral groove below the shoulder. Between shoulder and suture there is one prominent spiral rib and many finer spiral riblets. Axial ribs present on body whorl below the shoulder, varying from obsolete to strong, sometimes only evident as nodules on the shoulder. Spiral grooves on base of body whorl. Outer lip reflected, inner edge either smooth or toothed. Columellar shield with narrow, central spiral ridge, and varying from smooth to lirate and nodulose, the lirae sometimes extending to the parietal wall. Umbilicus open, columellar shield margin deeply indented. False umbilicus almost closed. Colour fawn, with 3 or 4 spiral rows of squarish brown patches. Columella white, outer lip white with five dark brown patches externally.

Size: Up to 90 mm, typically 70 mm in length.

Distribution: Caloundra, Qld, to Gabo island, Vic. Also New Zealand.

Habitat: Taken in 50-500 m. Common.

Comparison: Distinguished by the deeply indented margin of the columellar shield.

Synonym: Xenogalea thomsoni palinodia Iredale, 1931 was applied to small, stout, strongly sculptured shells of this species.

Remarks: This species is variable in sculptural detail, but fairly consistent in shape. Specimens with two varices are not uncommon.

Figs. 1,2: Off Norah Head, NSW (DLB2518)


Copyright Des Beechey 2000