Electro-Voice Model 726 "Cardyne I" Microphone
The Electro-Voice model 726 was a dynamic microphone which featured a cardioid (heart-shaped) directional pattern for noise and feedback rejection, hence, the "Cardyne" name.  It was recommended for recording, public address, and communications applications and was sold in the 1950's and 60's for about $45.00, a moderate price at the time.  There was a "Cardyne II" version (model 731) of similar appearance, but with better frequency response, for about $10.00 more.