Authorities disagree on the nature of this stop. Wedgwood provides the most complete description: The stop invented and so named by Mr. Hope-Jones is a Flute of soft tone. It is composed of open rectangular wood pipes. The mouth, which is very long, is verticaly placed - i.e., instead of running across the pipe in the usual direction, is parallel with the sides of the pipe. The wind is carried up one corner of the pipe for a considerable distance, and blown in a thin sheet across the body of the pipe into the mouth. The lip is inverted. The sole example is at [the church of] St. George, Westcombe Park, Blackheath [England]. The name Tibia Mollis is also employed by Mr. John H. Compton, of Nottingham [England], to denote a variety of his Tibia Minor. The mouth is less wide, and the tone more subdued than that of the parent stop.
Tibia Mollis 4', Echo; Town Hall, Melbourne, Victoria, Australia; Hill, Norman & Beard 1929. (This example was of wood; it is not known whether it was of the Hope-Jones type. The Echo division was removed sometime after 1939, but most of its pipework is reportedly intact.)