Black Mask Detective Magazine

Black Mask Detective Magazine was a long running pulp fiction magazine published in the U.S. It started out in Apr 1920 as The Black Mask and carried a range of stories including westerns, adventure, mystery and crime. In the mid 1920s it began to focus on detective stories. The magazine went through several name changes, Black Mask, then Black Mask Detective and finally Black Mask Detective Magazine for its Jul 1951 issue, which was ironically also its last one.

This last issue is also the one of relevance to Agatha Christie. Over the course of its print run, it only carried one story by Christie:
 * vol. 36 no. 2, Jul 1951 - The Face of Helen.