[EDIT] This could be it, from LIFE in 1946: http://books.google.com/books?id=WUkEAAAAMBAJ&pg=PA48. The pattern looks about right, and McKelvy appears in the ad. So maybe it was ceramic from 1939 until sometime 1946-56, then glass?
Picked this one up at a local antique store a few weeks back. At the time I did a quick search and thought it was from the '40s. The markings are a bit different than the OP's.