Shell conical with small, backwardly curving apex nearly centrally placed and with numerous radial ridges. A lanceolate opening lies on the anterior slope near the apex, in empty shells seen to be partly blocked by a septum which internally separates the apical part of the shell from the region of the slit. The apex of the shell lies posteriorly on the right and ends in a spiral of one whorl. There are 19-25 radial ridges; these are crossed by other ridges lying irregularly parallel to the apertural plane and more prominent near the oval aperture. White-cream; white spots (pits plugged with dirt) lie in the furrows between the ridges. Up to 7 mm long, 5 mm broad, 4 mm high.
The snout is broad; at its base lie the two cephalic tentacles, each with an eye basally on a lateral eye stalk, the tentacle on the right with an additional bifid tentacle behind it. The foot is oval, has no operculum, and carries 20-23 epipodial tentacles, the more posterior ones longer than the others. The body is white. The mantle skirt is slit under the apical opening.

Shell conical, laterally compressed, medium in size, generally not exceed¬ing 12 mm. in length, usually high, but varying in height from 00% to 85 %> of the length in adult specimens. Color uniformly white, externally rather dull, internally glossy, the majority of the specimens being translucent. Base narrowly elliptical. Anterior slope slightly convex, posterior slope straight or very slightly concave. Apical whorls one and one-half, at the top and a little behind the middle of the shell, bent backwards and downwards against the posterior slope and turned toward the right. The surface of the apical whorls is slightly rough, without ribs but with several rows of punetules radiating from the apex and continuing to the margin over the rest of the shell where new row's also ap¬pear. Fissure high on the posterior slope immediately below the summit, tapering above, enlarging near its lower extremity to contract again at the end. The surface is sculptured with from 21 to 26 primary ribs, starting at the base of the apical whorls, between each two of which a secondary rib appears lower down; sometimes a third series of ribs appears between the other two. The strength of the sculpture varies a great deal, even among individuals in the same locality. The ribs may be strong or weak, sometimes so weak that they hardly stand out from the surface; in the former case they may be slightly beaded. There is no true concentric sculpture, but some of the lines of growth decussate the surface. Between the primary and secondary ribs there are generally one, two or three rows of chalky-white punctules, some of these being a continuation from the apical whorls. Margin sharp, crenulated, the projections caused by the primary ribs being bolder than those caused by the intermediate ribs. Inside of the shell porcellaneous-white and glossy, sometimes nacreous. In strongly sculp¬tured shells the primary ribs are marked by radiating translucent grooves. The rows of punctules on the outside show through as radiating series of points. Septum narrow, generally strongly convex, producing with the walls of the shell a funnel-like formation and extending a little beyond the end of the fissure. From the lower end of the fissure a shallow and fine groove extends to, or nearly to, the margin of the shell and is bounded on either side by a low ridge or callosity which is a continuation of the side of the septum at its point of attachment to the shell. The septum is sometimes buttressed on each side by a prop. A triangular shallow depression is formed on each side at the base of the septum, bounded by the septum, the prop and the sides of the shell. Forbes and Hanley described the animal as follows: "The animal is white. The head, which is tumid but short, bears two rather obtuse subulate stout tentacula, with the eyes, which are very large, on prominent bulgings, or short peduncles at their external bases. The mantle is simple-edged. The foot is oblong and not steep or high-sided; at its junction with the body there are on each side, six or seven short cirrhi, and an odd one, larger than the rest, and behind them on the left side. There are no cirrhi posteriorly. From the anal cleft projects a conspicuous truncated sheath-like membrane, open in front, where are three or more retractile papillae. The branchiae are distinctly visible in the cavity behind the head." Pelseneer and Rammelmeyer have made very careful anatomical studies of this species. The radula has been studied several times: for instance, by H. Friele. Length 11,25 mm; Width 7,5 mm; Height 8 mm.

As a consequence of its wide distribution and variation in shell characters, several names have been applied to this species. However, specimens from a single locality frequently show most of the variations that have been reported separately from various parts of its range. Hence the names that have been used for these several variations have to be considered as synonymous. The sculpture varies greatly, even on specimens from a single locality; for example, the ribs may be weak or well developed. There may be many or few rows of conspicuous punctules or these punctules may be relatively indistinct or even absent. The buttresses or props to the septum are generally, though not always, absent in young individuals and generally, though not invariably, present in adult forms. So far as I can determine, these variations exist wherever this species is known to occur. In particular, it has been held that the European and North American forms are distinct, either as species or subspecies, but in an examination of a large series of specimens from both sides of the Atlantic, no difference could be found which would permit such a separation.

P. noachina may be dredged, not uncommonly, on stones from hard bottoms from 20 to about 150 m deep. It occurs from the north coast of Ireland round Scotland to Rockall and the Northern Isles and south to Yorkshire in the North Sea. Abroad it is circumpolar in distribution, becoming intertidal in high latitudes. It is probably a grazer or detritivore.

In the eastern Atlantic from Franz Josef Land, in the Arctic Ocean south to Scotland and northern England and on the continent along the coast of Norway south to Spain. In the western Atlantic from Greenland and the Melville Peninsula, and from Hudson Bay south to Cape Cod (Farfante, 1947), Magellan Strait, Patagonia, and the Falkland Islands (Odhner, 1912). In the eastern Pacific from Point Barrow, the Aleutians, the Shumagins, and south of Juneau, This species is new to Arctic Alaska.

Range. EASTERN ATLANTIC: Franz Josef Land in the Arctic Ocean south to Scotland and northern England and on the continent along the coast of Norway and south to Spain.

WESTERN ATLANTIC: from Greenland and Melville Peninsula, Hudson Bay, south to Cape Cod. It has also been recorded from the south Indian Ocean. The records from western North America are definitely known to be based upon other species. Records from the Sea of Okhotsk, Korea and Japan should all be restudied to determine if they are P. noachina or a closely allied species. Puncturella noachina is a widely distributed species extending as it does from Franz Joseph Land in the Arctic Ocean, to off Spain in the Eastern Atlantic and west to the coast of North America from Greenland and North Canada to Cape Cod. It also occurs under various ecological conditions and in depths from near the low water line to 1105 fathoms.