I feel the need to question this det. See remarks comments in sp. page.

Well these two "species" both have the same ridge counts and shapes, and largely the same (and virtually unique) color pattern. Liljeblad separates them by "M. trifasciata always has the elytra terminating with black whereas M. sexnotata always requires a pale apex", so this ones does key to M. sexnotata.

But as we discussed with other tumblers, much of the family, and certainly this tribe, seems poorly defined, with many seemingly similar "species", based on small samples (apprently only 2 or 3 in the case of M. sexnotata). Wish we knew if Dr. Jackman had revised his own unpublished thoughts on the validity of M. sexnotata. I received at least one correspondance from him expressing a nominclature difference which he certainly believed but had yet to publish ( here's at least the third determination by Dr. Jackman that seems like perhaps he was thinking of a "species pair" (same ridges/counts again too)). I'll try to contact some professionals working this family to see if there's more accurate keys / species lists, published or not.