The most recent comprehensive treatment of this Indo-Pacific genus ¹) is that of TESCH (1918, p. 78-82). Here seven species are recognised with the reservation that M. eydouxi H. Milne Edwards and M. thukuhar (Owen) are possibly not distinct. In 1936 (TWEEDIE 1936, p. 49) I questioned the validity of the character used to separate M. latifrons (White) and M. maculatus H. M.-E., the relation of carapace length and breadth, and placed maculatus in the synonymy of latifrons.