Shell. A semitransparent, fusiform, and somewhat glossy shell with rather blunt apex and not much elongated base. The shell as a whole has an apical angle of 40-45° but that of the protoconch is 80-90° so thai the spire is cyrtoconoid. There arc 8-9 rather tumid whorls meeting at deep, incised sutures lying below the periphery of the upper whorl and made wavy by the ends of costae. The ornament comprises costae, spiral ridges, and growth lines. The costae are flexuous, orthocline or prosocline at the adapical suture, becoming gently opisthocline; they are narrow — much less than the intervening spaces — cross the whorls of the spire, but disappear near the periphery or on the basal half of the last whorl. There is a labial varix (often in the form of 2 approximated costae), then a short stretch in which costae arc reduced or absent, then a regular series of up to 14 on the last whorl, 14 or 15 on the penult, 15-16 on the rest up to the protoconch. The spiral ridges are numerous, about 50 on the last whorl, dropping to (approximately) 22. 18, 12. up the spire. They are low, a rounded sirap-shape, rather broader than the spaces between. They cross the costae making them a little nodose, and are themselves a little tuberculate where crossed by growth lines, which are prosocline at the adapical suture but become orthocline.
The protoconch has about 3.5 whorls, rather less tumid than those elsewhere, and with shallow sutures set close to the periphery of the upper whorl, so that the protoconch appears in profile as a triangular apical knob. Whorl 1 bears many spiral lines with lateral spurs, whorls 2, 3, show a more complex pattern, the adapical half bearing a number of zigzag lines, the lower half a series of thin, more or less axial ones. Basally, just above the suture, is a thin spiral cord, and between it and the suture a further series of irregular wavy lines may be visible. The axial ridges arc usually orthocline, but may be markedly prosocline, and their direction can change from one whorl to the next. The junction with the postlarval shell is abrupt and crescentic, showing the presence of a peripheral beak in the larval shell. The initial whorl is 350-400 µm in diameter, the whole protoconch 1250-1300 µm.
Aperture. An elongated oval, pinched adapically, narrowing below to a siphonal canal, and surrounded by a peristome placed in a slightly prosocline plane. The outer lip arises below the periphery of the last whorl, perpendicular to the surface, and curves smoothly to the distal end of the siphonal canal, its edge buttressed by the varix. The columella is short, its lip everted, with a rather thick, upstanding edge; the parietal lip is extensive, has no thick edge, and rises over the origin of the outer lip. The siphonal canal is short, widely open, twisted to face right. The columella has a basal ridge, is grooved longitudinally, may have 2 teeth on the adapical side of the ridge; the outer lip has about 6 ridge-like teeth internally, that by the canal the largest. These features are absent in juveniles.
Colour. White, sometimes with brown markings; protoconch golden yellow. Size: Up to 8 x 4 mm. Last whorl = 65-75% of total shell height; aperture 45-55% of shell height.
Animal. There is no snout, the head forming a transverse ledge supporting the tentacles and with the mouth ( = opening of a proboscis sac) underneath. The tentacles are short, close-set, have blunt tips and a basal eye laterally. Except for the siphon, the mantle is plain-edged. Males have a rather long penis behind the right tentacle.
The foot is long and narrow with a truncated double edge anteriorly, and pointed behind. It carries an oval operculum.
Geographical distribution. This species is apparently widespread throughout the North Atlantic from Scandinavia to North America. Since it occurs in rather deep water it has been recorded, in the area dealt with, only in a few places north and west of Scotland and Ireland, and in sea area Sole.
Habitat. Soft bottoms 150-2000 m deep.
Breeding and growth. The sexes may be told apart by the penis of the male. Bouchet (1977) has shown that this species has a free larva which must have a relatively long life before settling. A larva perhaps belonging to this species was taken in Biscayan plankton and described by Pelseneer (1906); it was said to have a 4-lobed velum, which is consistent with a lengthy planktotrophic life.
Notes. This species has frequently been confused with Pyrene costulata (Cantraine, 1835) (= Amphissa costulata) but according to Waren (1980) the two are distinct since A. costulata has direct development. This contusion may invalidate the apparent distribution of both.

From the Lofoten Is. southwards on the outer banks off the Norwegian coast in 150-700 m; along the continental slope of the British Isles, the Bay of Biscay and south to 31°43 N (MONACO st 116); the bathyal of the Mediterranean and the Azores; S of Iceland (Thorson 1941:75, and INGOLF material in ZMC); also off northern N America south to North Carolina.

The present species has usually been known under the name Amphissa costulata or A. haliaeeti. The name of Cantraine (1835) is however preoccupied by Fusus costulatus Lamarck, 1822. The second available name, B. acutecostatum was used by Locard (1897) without any comments, although Watson (1886) who had received specimens supposed to be acutecostatum from Seguenza, wrote that he had "no doubts that the Buccinum acutecostatum is not the Columbella haliaeeti Jeffreys" Dautzenberg (1927) on the contrary, said he could see no differences between Recent specimens and fossil acutecostata that he had received from Montcrosato. He apparently used the name costulata because it escaped his notice that it was preoccupied. None of these authors figured any fossil specimens to support their conclusions.
Through the kindness of S. Palazzi, we have been able to examine fossil specimens from S Italy (Boretto) that agree well with Philippics description and occur in deposits having a similar fauna as Philippics specimens. We have not been able to find any difference from Recent specimens and conclude that acutecostatum is the correct name for the Recent species too.