Looks like a crest form of perhaps M. elongata.

Nice one Fred --- I think you tagged it...Thanks!....and I found a pretty cool site as a result of your answer.

Copy and paste this [Doña Púa] into Google and the first site that comes up has some excellent photos/ids of some cactus:

Doña Púa

Lots of you vets probably know this one, but it was new to my eyes :-)

The Mammillaria you id'ed is on the Doña Púa site too...

Now I need to go back to that site and see if there were any succ pics/ids

Thanks again Fred