In Taxon 00(00). 1-16 there is a new DNA study that attempts to resolve the issues raised in previous studies, such as that of Butterworth (2002, 2004 with Wallace) and others, which appeared to link Cochemeia species with many other species in several Series in the Hunt and Luthy classifications.
It appears to be pretty sound, and resolves many things of the Baja species (leaving the "green" Mamms where they are, close to M. bocensis). Most other Baja species, and some mainland species (sheldonii, grahamii, guelzowiana, saboe, goldii, haudeana, are transferred to a much larger Cochemiea genus.
Well worth reading, and no doubt more discussion will ensue.