Seven new members of the hamigeran family of diterpenoids have been isolated from the New Zealand marine sponge Hamigera tarangaensis. Among the new additions are hamigeran R (1), considered to be the first benzonitrile-based marine natural product, and hamigeran S (2), the first dimeric structure in the series. The formation of 1 and 2 is thought to occur via the reaction of hamigeran G with a nitrogen source, where the nitrile carbon of 1 is derived from the terpenoid skeleton.