Two new species of the genus Callochiton are described: C. sonchaensis sp. nov. from Vietnam and C. tongaensis sp. nov. from Tonga. They differ from other congeneric species in having a different number, shape, size and arrangement of grooves on the pleural areas of the intermediate and tail valves, the number of slits, the size of the dorsal spicules, and sometimes the coloration of the girdle. Absence of Callochiton in the Caribbean Sea and along the coasts of Central and North Americas was, perhaps, due to late advancement of species from this genus into the Tethys from the regions near Gondwana.