Shell. A rather tall and slender conical shell (apical angle 38-45°) drawn out basally into an extended siphonal canal. The fresh shell is glossy and a little transparent. The spire is mainly straight-sided, though often a little cyrtoconoid, and is markedly turreted by the presence of a concave subsutural area on each whorl and an adjacent spine on each costa. The whorls, of which there are about 7, meet at rather deep sutures placed far below the periphery of the upper one. The ornament comprises costae, spiral ridges and grooves, and growth lines. On the flat subsutural area the costae are low and lie in a prosocline direction, but at its abapical boundary they increase greatly in height and bend rather abruptly to run orthoclinally or even a little opisthoclinally. Each is laminar, the leading edge leaning appreciably towards the aperture and its crest made wavy by the spiral ridges and grooves which run over it. The edge is often made of multiple sheets. The breadth of each costa is less than the space between costae. On the spire the costae cross the whorls; on the last whorl they become low basally and form only small overlapping lamellae on the siphonal canal. The spiral ridges and grooves arc undulate in section and about equal in size. They are absent from the subsutural area of each whorl and from the siphonal canal. Spirals and costae interact so that the surface of the latter and their edge are flung into waves, highest at the shoulder of the whorl where a prominent tubercle is placed. There are 11-13 costae on the last whorl and 6-8 spiral ridges; on the penult the numbers are 12-14 costae and 3-5 ridges; on the antepenult 12-13 costae, 2-4 ridges and they decrease slowly towards the protoconch.
The protoconch has 1.25-1.75 whorls, 800-900 um across, smooth.
Aperture. Much as in muricatus but the siphonal canal (= c. 22% of total shell height) is less bent away from the apertural side of the shell and, on its columellar side, less than half its breadth is covered. The outer lip arises level with spiral ridge 4, exhibits a small anal sinus, a flat initial part corresponding to the subsutural area, and a rather flattened peripheral stretch. Where these two parts meet there may be an everted hollow spine and the whole length below that be flared outwards, depending upon whether a costa is developed along the lip (as is usual) or not. The edge is thin and wavy, the throat without teeth, though some depressions may underlie the ribs.
Colour, White or colourless, sometimes with a yellowish tint along the crests of the costae.
Size. 15x7 mm. Last whorl (including siphonal canal) = 70-75% of total shell height, aperture (with canal) = 60% of total shell height.
Animal. As in muricatus.
Colour. White.
Geographical distribution. A northern species which is found in Iceland and from the north of Norway as far south as the northern half of the British Isles, and further south at greater depths. It extends into the Skagerrak and reaches the Swedish west coast.
Habitat. Sublittoral on stony bottoms from a few metres deep at the northern end of its range to 300-400 m at the southern.
Food, breeding and growth. All unknown, but presumably the animals are carnivores and lay egg capsules from which juveniles hatch. Jeffreys (1867) mentioned a capsule laid on a bivalve shell.
Notes on Boreotrophon and Trophonopsis species. The original genus Trophon of Montfort, 1810 has now been split into a large number (Radwin & D'Attilio, 1976) of which only two concern us, Boreotrophon and Trophonopsis. They are distinguished from other neogastropod genera of the area by the long, rather delicate,, siphonal canal, predominantly axial ornament, and short, smooth protoconch. Boreotrophon shells have either no, or inconspicuous spiral decoration whereas (his is obvious in those belonging to Trophonopsis. The number and shape of the ribs separate the species in each genus relatively easily.
Whether there are really 4 species of trophonine muricids in British and Danish waters is uncertain. Marshall (1895) and Ankel (1936) have regarded B. truncates and B. clathratus as respectively the southern and northern forms of a single species clathratus, and the latter, following Chaster & Heathcote (1894) has also treated T. barvicensis as a variety of muricatus. This has also been proposed by Houart (1981). The verification or rebuttal of such ideas would call for examination of longer series than are available, especially from localities in high latitudes.

T barvicensis is often very common on the shelf off S Norway, where it occurs together with T clavatus in large numbers. Some young specimens may then be difficult to distinguish from that species, but they are quite rare and can be separated by having a microsculpture of scattered tubercles on the protoconch, while T barvicensis has these tubercles arranged in lines.
We have not seen any unquestionable Mediterranean specimens. Some specimens reported on by Di Geronimo & Panetta (1973) and Franchini & Frilli (1970), determined as T richardi, resemble T barvicensis closely, but we have seen all intermediates between these specimens and T. muricatus from closely-situated localities. (Similar observations have been made by Chaster (1898) and Chaster & Heathcote (1894) in the British Isles.) Therefore we are not certain if T barvicensis lives in the Mediterranean. The question arises that T. barvicensis may be only a deep-water form of T muricatus, an assumption that is supported by the doubts expressed by Chaster (1898). However, in Scandinavia barvicensis occurs more shallowly, from 50 m, thus occupying depths where muricatus should be expected, yet barvicensis does not change form. The problem can, however, not be considered settled.
Some specimens from the Azores resemble T barvicensis closely, but have more convex larval whorls, they are more spiny and occasionally have a coloured shell. This may be a local form of barvicensis, but because of the differences mentioned above and the geographical separation, we prefer to keep it separate, at least until we know if T barvicensis occurs on any of the intermediate sea-mounts.

From W Finmark, N Norway (G.O. Sars, 1878), Iceland (Thorson, 1941), southwards on the shelf and in coastal waters to off Morocco (Locard, 1897), where it occurs in the upper bathyal zone.