This is the 1938 marbled beetle version of the Admiral 6M, the model 398-6M
The model number prefix determined the cabinet version;
396 for Brown Walnut, 397 for Ivory Plaskon, and 398 for Beetle plastic.
The slide-rule reverse-painted glass dial is trimmed with a brass escutcheon.
Beetle radios, like the plaskon radio cabinets, commonly suffered from stress cracks.
Continental Radio & Television Corp. made this radio for Admiral.
Schematics were published in Vol 11 of the Riders manuals.