Ṡ (lowercase ṡẛ) is a letter of the Latin alphabet, formed by S with the addition of a dot above.
Irish orthography, the dot was used only for ẛ ṡ, while the following h was used for ch ph th; lenition of other letters was not indicated. Later the two systems spread to the entire set of lenitable consonants and competed with each other. Eventually the standard practice was to use the dot when writing in Gaelic script and the following h when writing in antiqua. Thus ċ and ch represent the same phonetic element in Modern Irish.