IUCN threat status:

Not evaluated

Comprehensive Description

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Description

Venustatrochus georgianus n.sp., Pl. X, fig. 68

 

Shell large, very thin, conical with biangulate whorls, the lower one coincident with the suture and forming the periphery of the last whorl; imperforate. Colour uniformly pale buff, with a greenish iridescence showing through. Whorls eight (seven in holotype), including the protoconch, which is small but projecting, slightly asymmetrical and consists of one unsculptured whorl somewhat immersed at the tip with a dull, slightly malleated white surface. First two post-nuclear whorls with two spiral threads above the peripheral carina and one below it; third with two above and two below, fourth with six above and three below, fifth with twelve above and ten below, penultimate with seventeen above and sixteen below, and base with about forty threads. The suture is ledged by the uppermost thread, and immediately below this on the later whorls there is a smooth, very slight concavity. The upper surface of the whorls is crossed by retractively arcuate fine dense threads which render the spirals minutely granular, but the basal spirals are smooth. Pillar plain, arcuate, much, thickened above and with a spreading callus which completely fills the umbilical area. Interior of aperture iridescent and delicately spirally grooved. Outer lip thin and sharp. Operculum horny, circular, multispiral, reddish brown.

 

Diameter 40.0 mm.; height 40.0 mm. (paratype).

 

Diameter 32.0 mm.; height 30.5 mm. (holotype).

 

The smaller specimen is selected for the holotype, since the other has the protoconch missing and the surface is eroded and encrusted.

 

The species resembles in a general way Dall's Calliostoma platinum (1889 a, p. 343, pl. VII, fig. 2) from near Santa Barbara Islands, 414 fathoms, California. Since the radula of platinum has not been described, actual relationship with georgianus cannot be claimed.

 

TYPE LOCALITY. St. 42. Off mouth of Cumberland Bay, South Georgia, from 6.3 miles N 89° E of, Jason Lt. to 4 miles N 39° E of Jason Lt., 1 Apr. 1926, 120-204 m.

 

DENTITION. Fig. H, 16, p. 190. (∞+1) + 16 + 1+16 +(1+∞).”

 

(Powell, 1951, 92-93)

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Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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