edmondson et al. distinguish several subtypes of pharyngeal consonant. pharyngeal or epiglottal stops and trills are usually produced by contracting the aryepiglottic folds of the larynx against the epiglottis. that articulation has been distinguished as "aryepiglottal". in pharyngeal fricatives, the root of the tongue is retracted against the back wall of the pharynx. in a few languages, such as achumawi, amis of taiwan and perhaps some of the salishan languages, the two movements are combined, with the aryepiglottic folds and epiglottis brought together and retracted against the pharyngeal wall, an articulation that has been termed "epiglotto-pharyngeal". the ipa does not have diacritics to distinguish this articulation from standard aryepiglottals; edmonson et al. use the "ad hoc", somewhat misleading, transcriptions and . there are, however, several diacritics for subtypes of pharyngeal sound among the voice quality symbols.