Little cluster of cacti

[tacrolimus]

Hello all.

I have some difficulties with this small cluster of cacti. The color of their bodies is dark as it appears in the picture.
As a guide it may be useful to point out that the vase is 5 cm in diameter.
Could you please tell me at least the genus to which it belongs?

Thanks as always for your help.
Luigi

[Astro]

Lobivia arachnacantha

[tacrolimus]

Thanks

Luigi