Description. Shell small to medium-sized, white under tan periostracum; spire moderately elevated, umbilicus filled by white callus pad, operculum with thin white calcareous layer, marked by groove along outer edge. Length 10-60 mm.
Type Locality and Type Specimens. Iceland, type material unknown (Bouchet and Warén, 1993:763). Natica clausa: type locality and type material unknown.
Distribution. Arctic Ocean, circumpolar; south in the eastern Pacific to San Diego (33°N); south in the North Atlantic to the Bay of Biscay, France, and North Carolina (Bouchet and Warén, 1993).
Habitat. Soft bottoms, from 0-200 m in the Arctic; at greater depths near southern range limits. There are 68 lots from southern California in the LACM collection, occurring at depths of 80-400 m.
Remarks. Natica affinis is a common member of the offshore assemblage in southern California. Specimens are small at maturity (length to 15 mm), compared to those from northern localities, which may approach a length of 60 mm.
This species is better known to authors treating the eastern Pacific under the name Natica clausa Broderip and Sowerby, 1829, from an unknown type locality, but Bouchet and War6n (1993:763) showed that usage of the older name is unavoidable. It has been treated in more detail by Bouchet and War6n and by Marincovich (1977:410), who cited numerous synonyms from type localities in the Arctic, North Atlantic and North Pacific.

As Natica clausa:
Diagnostic characters
Like Euspira species in the general aspect of the shell but umbilicus is closed by a thick pad of shelly material. Operculum white and glossy, with external calcareous layer.

Other characters
The shell of this species is a little thinner and more translucent than in Euspira species, retains more of the periostracal cover than they do and so is less glossy. There are 4-5 tumid whorls, and the short spire is often much eroded. The outer lip arises nearly normal to the surface of the last whorl. The development of shelly substance over the last whorl is much less than in Euspira species. Yellowish, the colour due to the periostracum, and the shell is white where that is worn. Up to 12 mm high. 10 mm broad (up to 60 x 50 mm in Arctic seas); last whorl occupies 85-90% of shell height, aperture about 70%.
The animal is cream and shows the same external features as do Euspira species.
C. clausa is distributed around the globe in Arctic waters, and extends south, at ever-increasing depths, to Portugal, the Mediterranean, North Carolina, California and Japan. In the Arctic it lives on soft substrata about 4 m deep, but reaches over 2000 m in temperate latitudes. Only a few animals have been found locally, in far northern British waters.
The egg collar of this species has been described by Thorson (1935): the egg capsules in it are arranged in only 3-4 rows, each with only one large egg in it which hatches as a juvenile.