Distribution. Cascadia abyssal plain, Oregon (44° 36.2' to 48° 21.8' N and 125° 33.0' to 128° 25.8' W), living at 2265-2850 m.
Description. Shell medium sized for the genus, up to 30.4 mm in length (holotype), length/width ratio 2.1—2.4. Shape slender, lanceolate, lightly built, lamellate; subsutural ramp broad, weakly sloping, weakly convex. Color dirty white, aperture white within. Spire very high with teleoconch of broad, weakly convex, strongly shouldered whorls; suture impressed.
Protoconch, early teleoconch whorls missing in all examined specimens, only four teleoconch whorls remaining in adult specimens. Axial sculpture of teleoconch whorls consisting of low, flattened lamellae, more strongly developed at shoulder, producing short, broadly open spines. Last whorl with 8-12 lamellae, similar on previous whorls, other axial sculpture of numerous growth striae. No spiral sculpture except very low P1, producing short, broadly open spines where crossed by axial lamellae. Aperture broadly ovate; columellar lip narrow, smooth, rim adherent; outer lip thin, smooth within. Siphonal canal long, straight, weakly bent to left, broadly open ventrally with low, obsolete axial lamellae over whole length. Operculum light brown, ovate, with apical nucleus.
Remarks. This new species is included in Boreotrophon and not in Abyssotrophon because of its more solid shell, its high axial lamellae and the lack of any spiral sculpture.
Boreotrophon cascadiensis differs from any known abyssal and other Boreotrophon species by its very long and straight, broadly open siphonal canal, combined with low, narrow axial lamellae ending as short, open spines on the shoulder, a very broad, weakly sloping subsutural ramp and a very high spire, although broken in all the numerous examined specimen of B. cascadiensis. It differs from Abyssotrophon christae Egorov, 1992, described from the Gulf of Alaska (Fig. 11M), in having a more solid and larger shell with fewer, broader and flatter lamellae, a broader, less horizontal shoulder ramp, and a comparatively narrower siphonal canal.
It differs from Abyssotrophon ivanovi Egorov, 1992, (Fig. UN) from the Kurile-Kamchatka trench in having a more solid and larger shell, a longer, straighter and comparatively narrower siphonal canal and straight axial lamellae, compared to the diagonally slanted axials in A ivanovi.
Etymology. Named after the Cascadia abyssal plain where the specimens were collected.