Summary
This present study is a companion report to the one published in this Journal , No. 6. January, 1963, which covered the genera Papustyla, Forcartia and Meliobba. The two genera, Megalacron and Rhytidoconcha, reviewed in this report occur in the Bismarck Archipelago with two species, M . boyeri F. & B., found only on Woodlark Id., off the north-east coast of New Guinea, and M. alfredi Cox from Buka and Bougainville Islands in the northern Solomon Islands.