Stenoma porphyrastis is a moth of the Depressariidae family. It is found in Guyana and French Guiana. The wingspan is 21-22 mm. The forewings are light brown with the markings suffused, deep purple. There is an elongate blotch along the costa from the base to near one-third, extended at the base to the dorsum, from its apex sending a transverse shade to the middle of the next fascia. There is an irregular fascia from the middle of the costa to two-fifths of the dorsum, extended as an irregular blotch along the dorsum to the tornus. A transverse spot is found on the end of the cell, resting on this blotch and there is an irregular curved subterminal fascia from three-fourths of the costa to the tornus, the posterior margin suffused into the termen or connected with it by suffused streaks on