I'm running slow with PC problems so someone may have already replied but HEM refers to Father Herman E. Mattingly, deceased, and his book, "The Mattingly Family in Early America". If you are working without access to his work, I would recommend you consider acquiring a copy. They aren't particularly expensive ($20 last I heard) and using it as a reference on the early family is almost essential. Not that the good father didn't make a few errors, he did, but they were few, to the best of my knowledge, and can be worked around quite easily. Meanwhile, I, and I suspect others, would be willing to help out where we can. Good luck on all this.