Listed only by Maclean, who provides the following description: This speciality of the now extinct Robert Morton Organ Co. is nowadays something of a collector's item among organ pipes, examples are few and far between. The writed is indebted to Mr. Roy Gorish, of Denver, for the following details of a sample in his possession. In general construction it is similar to the Tibia Clausa from which it differs in the shape of the mouth, which has a sharp-edged upper lip, unleathered, and is also tapered, widening from top to bottom. The scale of the middle C pipe is 2 3/4 x 3-2/8 [sic]. This peculiar construction probably favors the production of a dissonant upper harmonic not normally present in stopped-flute tone, which might conceivably give a suggestion of the muffled tang that is much a characteristic feature of stopped and muted horn notes. Reasonably successful attempts at reproducing the quality of muted horn notes, played pianissimo, can be found in stops like the Keraulophone amd Herbert Norman's Corno Flute. In its imitative capacity, the Robert Morton stop lays itself open to criticism on the grounds that its scale is too large for the production of pianissimo quality and, in proportion to its power, the tone is not brassy enough to give a realistic representation of the muted horn's fortissimo timbre. Nevertheless, this Muted Horn stop was highly esteemed for its characteristically Romantic flavor by many prominent theatre organists of the late twenties.