Mating of hard-shelled intermolt females was observed in the portunid Thalamita sima H. Milne Edwards in the laboratory. During SCUBA samplings over a 20-month period, specimens in copula were seasonally observed, but no pre- or postmolt guarding was seen. Females sampled from pairs in copula (N = 3) in the field were in intermolt. Captive males copulated readily with intermolt ovigerous and nonovigerous females, copulation being brief (1-2 min, mean 98.6 + 21.1 s, N = 11). Three females reared in isolation from immature instars after producing an initial sterile brood were able to mate while in the intermolt condition and subsequently produce fertile eggs. Field observations of the frequency of ovigerous females indicate that brooding occurs over an extended period, April-October, with females in the laboratory able to produce up to 7 broods. Reasons for this unusual mating strategy for a portunid are discussed in relation to possible predator interactions and the large number of broods in a single intermolt period in this species. In Brachyura, two basic patterns of mating occur, that is, soft-female mating, where mating occurs immediately after the molt of the female, and hard-female mating, where mating occurs during the intermolt (hardshelled) period of the female. Soft-female mating has, based on the complexity of the female genital ducts, been suggested to be a more primitive mating behavior (Hartnoll, 1968, 1969). Within the Grapsidae, Majidae, and Xanthidae, the type of mating behavior in relation to the female molt cycle varies among species (Hartnoll, 1969). In the Portunidae and Cancridae, however,