It could be a Standard Rectifier Corporation 240E10,R. It appears in this June 1960 catalog. The company seems to be defunct: it was registered in 1960 and then its registration was surrendered in 1964.
I also found a tabulation (also from 1961) which lists its characteristics on page 35 (pdf page 38).
As TypeIA suspected, this is a Standard Rectifier Corporation diode. The logo below is from Electronics, Feb 3, 1961, page 81.