Thank you, the plant is a new addition in my yard here in the Sonoran Desert, which features about 20 Mamms, 80+ other assorted cacti, and nearly 200 Agaves. I am an Agavephile myself, but have a peculiar affection for Mamms, as well. My first thought upon seeing this plant, was that it reminded me very much of my M. spinossissima, but of course it's too thick, so a thicker subspecies makes a lot of sense to me. From the pics I've just seen and as you suggest, it doesn't look quite right though, does it? Small spines are white as white can be. I'll be sure post additional pics when it blooms, though I'm not sure when that will be, since the plant is new to me.