I do find identifying very similar looking species from the Stylothelae extremely difficult.
I could do a "Fitz-Maurice" and simply say - just a form of M. crinita. That's easy, and the spine count of 3 central, of which lower 1 is hooked, and 12-15 white radial spines, fits well within its description. But that's because so many "species" have been lumped together into a broader species definition and so its characters are now broader too.
The description of M. mathildae doesn't fit the spine count of this plant, though the colouring does. But then, how reliable are spine counts? A lot of things, cultural as well as genetic can affect them.
I would want to see a flower, in bud and open, see what colour the stigma is, the petals, outer sepals, before I came to any conclusion on this one. Sorry.