The original description of Rebutia (Aylostera) tarvitaensis was published in Kakteen und andere Sukkulenten 28(4): 78, 1977, the journal of the Deutsche Kakteen-Gesellschaft, by Friedrich Ritter. The description is very brief but a little more detail, and a rather poor black and white photograph, are given in Ritter’s book “Kakteen in Südamerika”, vol. 2, pp. 608 & 783.

Here is the text in Latin as published, with my own English translation. You should look up the original description for more details.

Rebutia tarvitaensis Ritter spec. nov.
Ab Rebutia melachlora recedit corpore 2-3 cm crasso, in aetate elongato, viridi ; costis 13-15, dissolutis, tuberculis humilioribus, confertioribus; areolis 1,5 mm longis, inter se propinquius; spinis 7-9, solum marginalibus, 2,5-5 mm longis, adpressis, rufis. Floribus miniatis, ad 6 cm d i a m . ; seminibus paulum longioribus; habitat Tarvita Prov. Azurduy, Bolivia.
Collected as FR 773.

English translation

Rebutia tarvitaensis Ritter Spec. nov.
Differing from Rebutia melachlora in that the body is 2 – 3 cm thick, elongating with age, green; Ribs 13-15, low tubercles not well defined, crowded; areoles 1,5 mm long, close to each other; spines 7-9, marginal only, 2,5-5 mm long; adpressed, rufous. Flowers up to 6 cm diam. ; seeds a little longer; Habitat Tarvita Prov. Azurduy, Bolivia.
Collected as FR 773.