Rebutia violaciflora was first described by C. Backeberg in Blätter für Kakteenforschung, 1935 issue 8 (no page numbers). The description is given in German, English, Dutch and French, and there is a black-and-white photograph of a grafted cutting.
Here is the description in English as published. You should look up the original for further details and the photograph.
REBUTIA VIOLACIFLORA Bckbg. n. sp.
Solitary, dark yellowish green; small spheres about 2 cm in diam., very inconspicuous in its habitat. Crown depressed. Areoles small, 1 mm diameter, with yellowish white felt. Ca. 20 bristly, stiff, radiating dark golden yellow brown spines 3-25 mm long the centrals darker. Flowers ca. 3.5 cm long and 3 cm across, shining rosy violet, unusual, striking colour. Stamens white, 5 white stigmas. Occurrence: Salta (N. Argentina) between stones on mountain tops at 3000 m.