The Western Australian deep-water tonguesole Cynoglossus westraliensis n. sp. is described from off North West Cape, Western Australia, based on two specimens collected at a depth of 250 metres. The new species is characterised within the Cynoglossus carpenteri species group by the snout relatively long, bluntly rounded; head length 21-25% of SL, snout length 9.3-11.6% of SL (43.4-46.5% of HL); eyes not contiguous; corner of mouth nearer to posterior edge of opercle than to tip of snout; ocular side with 3 lateral lines, midlateral-line scales 111-115, scale rows between midlateral and dorsolateral lines 20, blind side without lateral lines; ctenoid scales on ocular side, cycloid scales on blind side; dorsal-fin-rays 120-126; anal-fin rays 105-106; caudal-fin rays 8; gill chamber and peritoneum black. A key to the species of the Cynoglossus carpenteri species-group is presented.