The descriptive note comes from item B0250 in :
Cowden, Robert H.
Concert and opera singers
A bibliography of biographical materials
Compiled by Robert H. Cowden
Westport, Connecticut: Greenwood Press, c1985, 278 p.
This is what Robert H. Cowden had to say:
Very helpful regarding artists who appeared with the Manhatten Opera Company which Hammerstein ran in competition with the Met.
© Robert H. Cowden
(c) 2013. Frank Greene. All rights reserved.