Coryphantha (Neolloydea) georgii?

Please help me identify this cactus. I think it's some Coryphantha (Neolloydea), maybe C. georgii? I found it in the south of the state San Luis Potosi (Santa Maria del Rio)

I think that this might be Coryphantha clavata. Santa Maria del Rio is close to the reported locations.
In Coryphantha by Dicht and Luthy is a comparison of C. clavata, C. ocatcantha and C. georgii. The differences are in the size of flower,s number of central spines and the disposition of the radial spines. I choose clavata because of the single central spine, the regular placement (disposition) of the radial spines, and the relatively small flowers.

Dear Chris,
thank you very much for your opinion! Maybe you're right, but
I have two C. clavata from Hidalgo. They look different and do not have a mace in shape.

That's interesting, as according to Dicht and Luthy, C. clavata doesn't come from Hidalgo! If they are right (and its the "bible" of Corys) then your "clavata" plants are probably C. octacantha. I have scanned the relevant section which compares the species of interest here. C. georgii is present in the area where you found your plant. It'd be interesting what you make of these. I saw C. georgii near Balnarea Lourdes some years ago. They weren't clavate and did have large flowers.

Dear Chris,
Thanks again! Now it became clear to me. Oh my god, for two years I was sure that I had a C. clavata from Hidalgo .

Dear Chris,
Look please. I have two plants from the Santha Maria del Rio. They both have a growth form clavate (not cylindrical-columnar)  and epidermis dark green (not grass-green) but the flowers are really small 3 cm.

I had a plant of C. clavata and it, and C. clavata v. stipitata. were both clavate. After all that is what the name means! So exactly why the "bible" says they are columnar.
Via Google I found this set of images, definitely clavate to me!
C. clavata

Dear Chris,
Good! I will agree with you. Thanks a lot!

And if you search for Coryphantha Santa Maria del Rio, it will lead you to iNaturalist. There you can search under 'plants' for 'coryphantha'. That will give you some photos, among them C. clavata. See https://www.inaturalist.org/places/santa-maria-del-rio-san-luis-potosi-mx#q=coryphantha

Wolter ten Hoeve.

Thanks Wolter,
I saw this page and looked at the pictures, but I still had doubts.