Shell medium-sized, consisting of 4,5 whorls, greyish white, very solid, smooth and glossy, with a moderately elevated spire. Apex blunt and rounded, protoconch about 2 mm in diameter, consisting of approximately 1,75 whorl, not delimited from the teleoconch. Spire whorls very slightly convex, with a thin suture. Last whorl representing more than 80% of total height. Aperture elongate, narrow, parallel-sided except at the adapical end where it tapers. Outer lip smooth inside, bordered externally by a broad, well delimited, evenly thickened labial varix, very slightly receding at its adapical end, forming there a moderately pronounced shoulder against the penultimate whorl. There are four columellar plaits, stout with a flattened crest, decreasing in size towards the abapical part of the columella, occupying two-thirds of the aperture length. No columellar callus.
Animal colourless, with a broad and short foot extending flat when crawling, reaching about the same length as the shell longitudinally and about 120% of the shell breadth transversally; the propodium with a broad transverse flap and, behind this, an opaque white glandular area visible by transparency. Head bifid as usual in marginellids, with long, slender and tapering tentacles, lacking eyes but presenting a distinct bulge on each side, at the base of the tentacles where eyes should normally be situated. Siphon large, extending anteriorly about one-third of shell length. Dimensions of holotype: 16.7 height x 8.2 mm diameter; of paratypes, 14.1 x 7.6 mm, 14.2 x 7.5mm, 14.3 x 7.5 mm.

Large species of the family Marginellidae, widely represented in tropical eastern Atlantic waters, are placed in the genera Marginella Lamarck, 1799, Glabella Swainson, 1840, Dentimargo Cossmann, 1899, Prunum Herrmannsen, 1852 and Volvarina Hinds, 1844 (Cossignani 2006). The first of these genera includes species with a prominent spire and a relatively wide opening without a pronounced labial denticle and without axial sculpture.
The majority of Marginella species (illustrated in Cossignani, 2006) live in shallow water, with a generally characteristic colour pattern. Only Marginella glabella (Linnaeus, 1758), from shallow water and very different from the species found in our material (Cossignani 2006: 115> 127). Marginella marocana and M. subturrita belong to a group of deep water species illustrated in Bouchet & Waren (1985: 274-275), of relatively large size (20-30 mm). Marginella carmenae n. sp. is clearly differentiated by the shape of the lip of uniform thickness (swollen in the central part and thinning at the ends in M. marocana) and by the elongated, parallel-sided aperture (very wide, almost oval in M. subturrita). A further difference is that in M. marocana the abapical columellar plait is continued as a ridge to the abapical end of the shell whereas it fades out at a short distance in Marginella carmenae n. sp. Marginella gustavoi, the only species so far with a Canarian deep-water type locality, has a still more globose apex, a shorter and stouter spire and considerably thinner outer lip and columellar plait, with a very broad aperture.
From the platform of NW Africa, comparable species would be M. adamkusi Bozzetti, 1994, which differs by being smaller (10 mm), with a prominent colour pattern and with a swelling in the upper third of the lip that could justify its assignment to Dentimargo. Marginella belcheri Hinds, 1844 is larger (18-20 mm) with a different colour pattern, has a much more pointed apex and the outer lip is thinning out at the adapical end (Goud & Neefs 1996).
In M. carmenae n. sp., no definite limit could be seen between protoconch and teleoconch, neither on the live taken specimens nor on more or less worn shells. The approximate limit is taken where growth lines start to be apparent on the shell surface.

TYPE LOCALITY. — Off NW Gran Canaria, 28°08.26'N, 15o51.99'W/28o08.47,N, 15°51.66'W, 470-485 m. OTHER MATERIAL EXAMINED. — 2 adult sh. and 1 juvenile, DW126; 1 adult spm., DW129; 3 immature spm, 9 sh. in early postlarval stage, DW130.