Hans Fruhstorfer describes: "M. rhetenor, already named by Cramer the 'blue elongate Atlas butterfly', has the apex of the forewing more produced than any other Morphid species; a characteristic, however, that partially disappears in the female, which more resembles that of cypris.

The male is one of the most brilliantly glossy species and has only a quite inconsiderable black apical spot and a white costal patch on the forewing.

The under surface is noteworthy for the contrast between the black basal area and a brown distal region, which are separated by a median band of a more or less pure white and of varying extent according to the locality.

The female (shown in the Seitz plate below) is bigger than the bright blue male and has a dark-brown upperside with a lighter brown outer edge.

inhabits the Amazon region, where Michael has observed it at Obidos in August and September, and Dr. Hahnel at Iquitos and Jurimaguas.