Shell rather large and thin, elongated; spire produced; sutures less deep than in B. tenue; whorls seven or eight, regularly convex, or slightly appressed, less gibbous or shouldered at the sutures than in B. tenue, and not carinated. Longitudinal folds very numerous, about nineteen, as broad as their interspaces, and most prominent near the suture; they are curved in a somewhat sigmoid form, and are sometimes, though rarely, interrupted, or have an intervening fold about the middle of the whorl. The striation of the surface has considerable resemblance to that of B. glaciate, the primary grooves being deep cut, with the intervening ridges depressed. But the grooving is far less regular than in that species; the primary grooves are more crowded near the suture, and the ridges less flattened. The secondary grooves on the surface of the primary ridges, are usually as fine as in B. glaciale, but often one or more of them becomes deeper, making the sculpture resemble more that of angulosum. Aperture oval, less than one-half the length of the shell, and narrower than in B. tenue. The columella does not project beyond the level of the anterior part of the outer lip, but rather falls short. The columella shows the usual three folds, but the middle fold being nearly longitudinal and parallel to the lowermost fold, the latter cannot be seen in a front view, but it is easily seen in an edge view of the columella (in broken specimens of the shell) separated from the marginal middle fold by a longitudinal sulcus. The first and second (uppermost and middle) folds are separated by a broad deep sinus. Periostraca thin, smooth, not ciliated. Length, 2.23; breadth, 1.2 in. (Stimpson.) TYPE in? Type locality not known to writer.
RANGE. Point Barrow, Arctic Ocean, south to Puget Sound; circumboreal.