During the preparation of the checklist of ostracods from Japan (Hanai et al., 1977), it was fully realized that the knowledge of the ostracods of the adjacent areas is indis pensable for understanding of the diversity that exists in Japanese ostracods. Many species have been known only from Japan, and these species may appear endemic mainly due to lack of information about the ostracods of the adjacent areas. Many of the Japanese thermophilic species, for example, may turn out to be merely a northerly extended fraction of the tropical species. Further, some of the true endemic species may be outliers which originated from the tropical species. Thus it became an urgent and logical next step to compile present taxonomic knowledge of the Southeast Asian ostracods.
Southeast Asia is one of the developing areas in terms of ostracod taxonomy, and certainly one of the farthest areas from the centers of taxonomic activity. In fact, present knowledge of the ostracods in this area has been based almost exclusively on the results of expeditions sent one after another by western institutions since the last century. Thus, this checklist may provide systematists with information on the geographical subareas, geological ages, taxonomic groups, etc., obtained by these expeditions, as well as point out where such information is lacking. Further, it is hoped that the kind of compilation offered here may be useful in future studies on particular aspects of evolution by regional taxonomists who are already in the field, holding an advantageous position of easy access to live material under natural conditions. Southeast Asia is cer-tainly one of the most interesting areas, in the sense emphasized by Gosline (1965), particularly for the "peripherally located" taxonomists, in terms of the problems of speciation, ecology, and zoogeography. In compiling this checklist, emphasis has been placed on the fact that the multidimensional and populational approach is the only way to attain proper classification of species group taxa and, hence, to adequately express further diversity even above the species level.