originally consisted of twenty distinct characters (feda), arranged in four series aicmí (plural of aicme "family"; compare aett). Each aicme was named after its first character (Aicme Beithe, Aicme hÚatha, Aicme Muine, Aicme Ailme, "the B Group", "the H Group", "the M Group", "the A Group"). Five additional letters were later introduced (mainly in the manuscript tradition), the so-called forfeda. The Ogam Tract also gives a variety of some hundred variant or secret modes of writing ogham (92 in the Book of Ballymote), for example, the "shield ogham" (ogam airenach, nr. 73). Even the Younger Futhark is introduced as a kind of "Viking ogham" (nrs. 91, 92). The four primary aicmí are, with their transcriptions in manuscript tradition and their names according to manuscript tradition in normalised Old Irish, followed by their Primitive Irish sound values, and their presumed original name in Primitive Irish in cases where the name's etymology is known: Right side/downward strokes B beith (*betwi-s) L luis (*lubsti-) F fearn (*wernā) S saille (*salik-s) N nuin Left side/upward strokes H úath (*osato-) D duir (*darek-s) T tinne C coll (*koslas) Q ceirt (*kʷer[x]tā) Across/pendicular strokes M muin G gort (*gorto-s) NG gétal (*gʷēdtlo-) Z straif or ? R ruis (*rudsti-) notches (vowels) A ailm O onn (*osno-) U úr E edad I idad A letter for p is conspicuously absent, since the phoneme was lost in Proto-Celtic, and the gap was not filled in Q-Celtic, and no sign was needed before loanwords from Latin containing p appeared in Irish (e.g., Patrick). Conversely, there is a letter for the labiovelar q (ᚊ ceirt), a phoneme lost in Old Irish. The base alphabet is, therefore, as it were, designed for Proto-Q-Celtic. Of the five forfeda or supplementary letters, only the first, ébad, regularly appears in inscriptions, but mostly with the value K (McManus, § 5.3, 1991), in the word koi (ᚕᚑᚔ "here"). The others, except for emancholl, have at most only one certain 'orthodox' (see below) inscription each. Due to their limited practical use, later ogamists turned the supplementary letters into a series of diphthongs, changing completely the values for pín and emancholl. This meant that the alphabet was once again without a letter for the 'P' sound, forcing the invention of the letter peithboc (soft 'B'), which appears in the manuscripts only. EA ébad , ; OI óir UI uillenn P, later IO pín (later iphín) , X