Description. Shell small, up to 11.5 mm in height, fusiform, of 6 slightly convex whorls; protoconch of about 1 1/2 convex whorls, with 5 to 6 spiral threads; suture impressed, slightly channelled; aperture elliptic; siphonal canal rather deep and short; parietal callus thin. Spiral ornamentation of 5 flat threads per whorl, about 20 on the last; axial sculpture of 14 rounded ribs (varices) that develop nodes when crossing the spiral threads. Periostracum translucent, very thin, producing a scaly appearance on the sulci between threads. Color brownish or reddish.
Operculum pale yellowish, ovate-elliptical, nucleus subterminal, thick rim, small attachment area towards left side.
Radula rachiglossate, central tooth with three cusps, the central cusp largest; lateral teeth with two large curved, hook-shaped cusps with an obsolete cusp close to the inner one. Penis large, flat, thick with a small papilla on the tip.

The shell is similar to M martensi, however, the protoconch of this species is distinctive, with axial threads instead of the typical spirals. Strebel (1905) included four Magellanic species in his new genus, i.e. the type G meridionalis, "G " martensi, "G " agnesia and "G " kobelti. The only species belonging to Glypteuthria is the type species. G agnesia is a synonym of Meteuthria martensi and G kobelti belongs in a different new genus proposed here: Falsimacme.
Powell (1951: 138, 1960: 148), Castellanos (1970: 98) and Dell (1972: 36) included Euthria acuminata Smith, 1915 in Glypteuthria', however, this is a columbellid (according to the radula illustrated in Fernandez & Castellanos, 1973), probably belonging in the genus Amphissa (sensu Rios, 1994: 124).
Castellanos (1970) included E. agnesia Strebel, 1905 in Glypteuthria. Fernandez & Castellanos (1973) included what they called E. agnesia Strebel, 1905 in the columbellid genus Pyrene. Later Castellanos (1982) described the new species Amphissa cancellata (Columbellidae) to include this material that she considered previously as E. agnesia.
Dell (1972) suggested Lachesis euthrioides Melvill & Standen, 1898 as a synonym, however this is a valid species, dealt with here in the new Prosiphiinae genus Argeneuthria.

Type locality. Portland Bay, St. Andrews Sound, 10 fms. [18.2 m] depth, and Sandy Point [Chile] in 9-10 fms. [16.4-18.2 m] depth.
Distribution. Only known from Tierra del Fuego and environs including the Straits of Magellan.