M. heyderi???

Someone on another forum was trying to ID this plant... anyone recognize it?

My view is that heyderi is a good suggestion.I don't know for sure which subspecies though, dont think it is ssp. gaumeri, sso. gummifera or ssp. meiacantha, could be ssp. hemisphaerica though, or perhaps simple heyderi ssp heyderi, though ssp. bullingtoniana has yellow flowers. Whichever it is, it has darker than the typical spines. Nice.

I think it is heydery subsp macdougalii

I believe this to be heyderi gaumeri and I offer the plant below, Rep 1897, San Bruno, 25m, Yucatan, for comparison.

Thanks guys... That's a lot of suggestions. I haven't had a chance to do any research... but will.

Tam, I know there's a lot of variation in populations and am really still learning, but the radials on yours number a pretty consistant twelve and are also fairly evenly spaced on just about all the areoles. The centrals are also not very distinct or prominent in the photo.
On the plant in question, radials number 13-16, are not evenly spaced around the areole with some real close and others spaced far apart and the Centrals are very obvious in the photos... being Much thicker than the radials and Black where the radials are white tipped with a reddish brown or all reddish brown to almost black.
That all could just be variations... .You guys would know better than I would.

The Stigma also looks a lot larger ... here's another image

The flowers look distinctly yellow, which would suggest, as Ento proposes, heyderi ssp. macdougalii. The description in Pilbean says 10-12 radial spines, lower stronger brown or black at the tips. However, I think this plant is a bit more variable. See below a couple of photos of it in habitat in Southern Arizona, last year.
I can certainly see some areoles which have 12 radial spines, but there are some with fewer and some with more.



and a little closer...



However, Reppenhagen says that gaumeri can have up to 19 radial spines, so I think to try to separate just on radial spine count is difficult. The flower colour perhaps is at least as significant.