The straight-sided demitasse shape was introduced in the mid-1930's. The ivory sets pictured here are from that time.
In late 1938 and early 1939, the shape was picked up and produced in Lu-Ray glazes. Shortly thereafter, a new ovoid shape AD set was added to the Lu-Ray line and the straight-sided shape was dropped from the line.
Lu-Ray collectors refer to these as "chocolate" set pieces to distinguish them from the later ovoid shape.
The following are from the collection of Greg and Teresa Benkert.