The two new species described in this paper are widely distributed in the tropical south-western Pacific; they have been found on the upper continental shelf of the area, around New Caledonia, westward to Chesterfield Islands and Lord Howe Ridge, southward to northern part of Norfolk Ridge, north- and eastward to Vanuatu, Fiji and Tonga islands. They belong to two often confused genera of subfamily Protocardiinae (sensu Keen 1980), Frigidocardium Habe, 1951 and Microcardium Thiele, 1934, that are briefly characterized herein. Frigidocardium valdentatum n. sp. is characterized by the peculiar sculpture of mid-posterior slope ending in strongly dentate margin. Frigidocardium kirana is a similar species with lower outer sculpture, more asymmetrical shape and rather strong umbonoventral fold; it is first recorded here from the tropical Southwest Pacific and Mascarene islands. Diagnostic features of Microcardium trapezoidale n. sp. include rather high trapezoidal shape and posterior sculptural area extending on 2/5 of shell length, with an anterior limit almost parallel to radial ribs in the adult and well-developed, non lamellous sculpture in the rib interstices. A comparative review of all Recent Microcardium species in the Indo-West Pacific is given, to place the new species in the context of the genus. Five Microcardium species are presently known in this area: M. gilchristi from southern Africa, M. simillimum n. comb. (for Cardium (Fragum) simillimum) from Sri Lanka and Mascarene Plateau, M. sakuraii from Japan and the Philippines (new record), M. aequiliratum from the Philippines, and M. tenuilamellosum from the Philippines and Solomon Islands (new record).
Mollusca, Bivalvia, Cardiidae, Frigidocardium, Microcardium, Indo-Pacific, new species.