If you read the original description that Dean posted above, it says that orizabensis has cream or white throat and anterior ventrals (as opposed to "pink").
An example of typical erebennus ventrals from further north (Cd. Victoria, Tamaulipas) is shown above. Here the ventrals are clearly orange/pinkish in color. I don't know what color the anterior ventrals of a coastal Mexican melanurus would be.
As for orizabensis having white anterior ventrals and throat, this is in part what suggests to me that its affinites lie with the Pacific coast form rubidus. Does that make this rubidus? Another of the many questions in Mexican herpetology that need to be answered! Anyone looking for an MS project?