ID help needed please, possible melocactus?

[ange]

Hello All,

Please could anyone help identify this lovely cactus?
I don't have the knowledge to positively identify it myself, but it has gone downhill since I re potted it and an identification could help me with a recovery plan as well as general care if it pulls through!

Its spines are quite distinctive with the lowermost spine being longer than the others. I don't know how old it is but it's about 4 inches in diameter.

Many thanks

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[teo]

I have one very much like it and it's labeled Melocactus zehentneri (although I'm not quite sure that it is - it has not yet grown a cephalium)

[ange]

Thank you teo, yes I find it's so hard to tell when they're immature, they can look so different to the adults.