Mangelia with shell rounded, reddish-tawney, zoned with white; nuclear whorl (decollate); normally S, elongate-subrotund, with impressed sutures; with radial obtuse nearly straight costae, about 15 in number, ascending the spire; with spiral sculpture ?(worn off); with pyriform aperture, anteriorly attenuated into a short canal; with outer lip posteriorly slightly sinuated; with inner lip conspicuous. (Translation.)

Shell slender, fusiform, white, with a brown band on the anal fasciole, and another a little in front of the periphery, the latter most conspicuous on the last whorl; nucleus smooth, initial part very small, the apex flattened, the whole nucleus of about two whorls, followed by five and a half sculptured whorls; axial sculpture of (on the last whorl fifteen) uniform, flexuous, low, rounded ribs, attenuated on the fasciole, undulating the suture between the earlier whorls and rapidly becoming obsolete on the base of the last whorl; spiral sculpture of fine striae on the fasciole, in front of it sharp grooves with wider interspaces which at first are threadlike, later flattened, and on the last whorl are reduced to rather close-set, feeble, fine spiral striae; suture appressed; anal notch feeble; canal short, straight, with no siphonal fasciole; aperture narrow, elongate; outer lip thin, sharp; pillar lip smooth, white, polished, attenuated at the canal; operculum absent: Length of shell 12 mm.; of last whorl 9,2 mm.; of aperture 6,0 mm.; maximum diameter of shell 4, 25 mm.
In sand, between tides, at Skidegate inlet, Queen Charlotte islands, B.C., collected by W. Spreadborough, in 1910.
This species was described by Carpenter, in the Annals and Magazine of Natural History for January, 1865, though the nude name had been printed earlier, in his supplementary report to the British Association on the Mollusca of the West Coast of North America. The unique type is in the collection of the U.S. National Museum and has never been figured. It is a beachworn shell with a decollate spire, and with the fine sculpture of the surface entirely removed by wear, so that it appears smooth except for the axial ribbing. It should not have been named without better material. However, after some study, the fresh shells collected by Mr. Spreadborough seem to be of the same species and differ only in their better state of preservation. As the shell has never been fully described or figured, a description and figure are now supplied for the benefit of students. Another form named by Carpenter from Neahbay, at the same time, is positively unrecognizable, even the genus cannot be determined of the so-called "Daphnella" effusa Cpr.
The animal of M. crebricostata is whitish, except a little brown stain on the siphon and a pair of very conspicuous black eyes almost at the tips of long slender subcylindric tentacles. There is a marked indentation mesially on the duplex anterior edge of the foot. There is no trace of an operculum.

Type locality, Neah Bay, Washington.
RANGE. Forrester Island, Alaska, to Monterey, California.