We describe a new species of Cyrtodactylus from Karkar Island, an active volcano off the northern coast of New Guinea. It is a member of the C. sermowaiensis species group, which is defined by the absence of enlarged precloacal and femoral scales and the absence of precloacal/femoral pores in males. This species group includes two other species, one of which is widespread along the northern mountain ranges of New Guinea, and the other of which is restricted to Manus Island. The new species differs from each of these in its larger size; more-tuberculate dorsum; wide, even bands across the dorsum; and uniformly brown crown of the head. Distributional data suggest that the C. sermowaiensis species group originated on the former islands of the South Caroline Arc, although only C. sermowaiensis currently occupies terranes derived from that arc. The other two species are now restricted to volcanic islands that originated independent of that arc, but the current restriction of our new species to Karkar Island seems likely to be a relictual distribution of a formerly wider range. The status of Karkar as an active volcano, and the explosive sterilization or virtual disappearance of other islands in the Bismarck Volcanic Arc, suggest that the new species could be at threat of immediate extinction should a similar explosive eruption occur on Karkar.

Key words: Bismarck Volcanic Arc, lizard, South Caroline Arc, trans-marine dispersal