Mistaken report of a third syllabary in Japanese
Imatto-canna (also written "Imatto canna" or "Jamatto canna") was a false Japanese syllabary reported by the German traveller Engelbert Kaempfer in his book "Amoenitatum exoticarum politico-physico-medicarum fasciculi V." (1712).
He wrote that Japan had three syllabaries: "firo-canna" (hiragana) and "catta-canna" (katakana), both used by commons, and "imatto-canna", used by nobles. However, the "imatto-canna" he believed to exist were just variant forms of hiragana called hentaigana. Being "hentaigana", they did not make up a cohesive or independent writing system, and were in often free variation with other "hiragana" characters. The only other Japanese syllabary besides hiragana and katakana is their precursor man'yōgana, use of which had died out well before 1712.
"Imatto-canna" was probably his transliteration of the word "yamato-gana", which actually means kana in general, both hiragana and katakana.