The original description (of Rebutia rafaellii) was published in the Italian journal Cactus & Co., 1 (9) 2005, pp. 215 to 221.
Here is an excerpt of the main points, but you should look up the full description for more details.
Rebutia brighignae Mosti & Papini sp. nov.
Typus – Holotypus: Argentina, Jujuy, Abra de Pives, WR 751. Cult. S. Mosti s. d. (FT) Ab R. oculata Werd. differt caulibus diametro minoribus (0.8-1.4 cm vice 1.8-2.2 cm) apice tomentosis; costis numero minoribus (9-10 vice 10-14); aculeis marginalibus minus numerosis (ad 9, rarius 10, numquam 12) ac minoribus (1.5-2 mm longis vice 4-5 mm), rectis reflexisque nec tortuosis patentibus; floribus flavis neque aurantiacis, tubo minore (1.5-2 cm vice 3.5-4 cm).
Stems: brevicylindrical to cylindrical with wool at the apex; dia. 0.8-1.4 cm, height 2-2.3 (-3) cm.
Epidermis: green to grey-green.
Tubercles: not very evident, flattened at the apex.
Areole: l. 2 mm ca. with short whitish felt.
Radial spines: 8-9 (-10); l. 1.5-2 mm; bulbous and brown at the base, apical half horn-colour or glassy white; straight and rigid and almost always pointing towards the stems.
Central spines: absent.
Flowers: l. 1.5-2 cm; w. 3.5-4 cm.
Flower tube: green, almost entirely covered with thick hair and bristles.
Segments of the perianth: lanceolate to lanceolate- spatulate and mucronate; dark yellow, with apical zone and central band reddish and more or less evident.
Filaments of the stamens: bright red to crimson.
Style: yellowish green.
Seed: not observed.