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The essential oils of fourteen liverwort specimens from nine species of the Jungermanniales have been examined as to their sesquiterpenes. The barbatenes prove to be present in detectable amounts in all but one species. Bazzanene is frequently found with the barbatenes and new chemical evidence does not support the previously assigned structure but is consistent with a structure diastereomeric to trichodiene. This is consistent with a biogenetic rationale for the barbatene skeleton. Anasterptene, a novel crystalline tetracyclic hydrocarbon, has been found in numerous oils, and chemical degradation established a common skeleton with myliol. The samples of genus Scapania elaborate sesquiterpenes of the enantiomeric humulene-longifolene sequence. New members of this group found are (−)-β-longipinene, (−)-longipipanol, and (+)-γ-himachalene. The related germacrene series is represented by a cadinene, (−)-α-ylangene, and (−)-sativene. A series of cis-fused selinenes have also been found, which are more closely allied to the germacrene-sativene group than to typical trans-fused selinenes. One of these selinenes is shown to be the same as the material previously designated as sibirene. Scapania undulata also elaborates (+)-α- and β-chamigrene, and a number of novel hydrocarbons of still unknown structure. more...