Above left again is M. antimachus. And right is M. prairiensis. Note the narrower face of M. antimachus. And the whitish hairs on the forefemur like snowii. M. prairiensis has almost no white hair and a wider face. Note the leg color differences again. 

Machimus snowii above left with fine white hair on the femur and the orange dominant tibias. On the right is notatus which is the darkest overall with almost all black legs.  Note the darker mystax and face as well. 

This is Machimus erythocnemius. More golden faced like prairiensis. No white hairs on femur. Legs look more coated with the hairs on this species. Femur rings of orange.