Diagnosis. Shell of medium size, biconic-fusiform. with a massive coronate spire, uniformly brown in colour. Subsutural fold with overhanging lower edge, slightly narrower than the peripheral keel. Both sculptural elements are very strong, gemmulate, and separated by very deeply excavated interspace. Spiral cords obsolete except for the lower part of the shell base and the canal. Columellar pleat distinct inside the aperture. Anal sinus deep, U-shaped.

Description of holotype. The shell is biconic-fusiform and rather thick and strong. The protoconch is missing and the upper part of teleoconch eroded. The beginning of the teleoconch is, however, clearly marked by a bluntly closed initial whorl. The teleoconch consists of 6 whorls separated by deeply channelled sutures. The profile of the spire is weakly convex. Whorls bear a very prominent subsutural fold and a strong peripheral keel. The subsutural fold is only slightly narrower than the keel, with downwards sloping surface and overhanging lower edge. A shallow groove borders the" rather sharp, wide and wavy upper edge of the fold, that covers the upper suture. Both sculptural elements become relatively less prominent towards the body whorl. They are covered by longitudinally elongate gemmules which are slightly oblique on the subsutural fold and arcuate on the peripheral keel. The number and position of gemmules on the fold more or less correspond to those on the keel. Gemmules on the peripheral keel become less distinct and, finally, obsolete on the body whorl. There are 34 gemmules on the penultimate whorl and 42 on the body. The subsutural fold is separated from the keel by very deeply excavated, smooth, asymmetrical interspace, the deepest part of which is situated just below the fold. Both subsutural fold and peripheral keel bear 1-2 very indistinct spiral cords. The keel on all whorls is set close to the lower suture, and the distance from the keel to the suture is less than to the subsutural fold. Spiral cords are absent on the spire whorls. The body whorl occupies about 2/3 of the shell height. Its periphery below the keel and the upper shell base are smooth, and only the lower part of the shell base and the canal are covered by weak and narrow spiral cords (about 20). The aperture is narrowly oval. The inner lip is covered by a thick while callus with longitudinal wrinkles near its edge. The columellar pleat is superficially obsolete, but well seen inside the aperture. The outer lip strongly projects forward below the sinus. The anal sinus is deep, U-shaped, with almost parallel and somewhat reflexed edges. The sinus is directed adapically.
Shell height 28.0 mm, body whorl height 18.4 mm, aperture height 15.4 mm, shell di¬ameter 10.2 mm. The shell is covered by rather thick brown periostracum.

The paratype is slightly larger (29.5 x 10.6 mm) but in not so good condition. It differs from the holotype by a broader subsutural fold even exceeding the keel in width, and stronger gemmules. which are quite distinct on the body whorl.
This species is very similar to G. hertzeli (Martin, 1933) (originally described (Martin, 1933, p. 21, pl. 3, figs 16, 16a) as Bathytoma) from Mio-Pliocene (see Beets, 1953) deposits of Buton (Butung) Island, Indonesia, and apparently represents a direct descendant of that species. The main difference between these species is that the subsutural fold in G. hertzeli is much narrower than the peripheral keel, whereas in G. karubar these sculptural elements are of approximately equal width.
G. karubar can be very easily distinguished from other species of the genus by the strong peripheral keel and subsutural fold with a very deeply excavated surface between them, and weakly developed spiral cords, which are present only on the lower part of the shell base and canal.

Distribution. Tanimbar Islands, Arafura Sea, dead in 552-620 m.