Den. atroviolaceum ?
IOSPE PHOTOS
This species belongs to the Latouria section.
Moderate light, warm to hot temps, media should not be allowed to dry out. Slightly drier in winter, tho media should still not dry completely.
I have read that Latouria Dens especially do not like their roots messed with,and as such, they are frequently potted in gravely (inorganic, but porous for moisture retention) media - and roots snug in pot. I have mine potted in a combo of pumice and perlite. Tho I am sure others grow these succesfully in bark, chc mixes, s/h.
I was a bit intimidated by this type of Den initially, but I have a few of them (including atroviolaceum, tho I have the pygmy variety) and they have been good growers and bloomers for me.