Abstract
Pronounced geographic variation in meristic characters is found in two Southeast Asian cyprinid species, Puntioplites proctozysron and Puntioplites waandersi.When local populations of each species are combined with other conspecific populations, these two forms overlap in all meristic and morphological characters examined.The only pheno-typically detectable difference between the two is the nature of the principal simple anal ray;the ray is serrated in P. proctozysron and entire in P. waandersi.This difference is shown not to represent individual or sexual dimorphism within a species.P. proctozysron and P. waandersi are considered to be distinct species directly differentiated from a common ancestor belonging to the same genus, Puntioplites, which is distinct from the genus Puntius.
Zoogeographical examination suggests the occurrence of Puntioplites waandersi through-out the continental and insular sections of Southeast Asia in the lower Tertiary or earlier, when these two sections constituted a continuous landmass, and subsequent isolation of continental populations in the middle Mekong basin.The present geographic range of Puntioplites proctozysron, being restricted to the continental section, seems to indicate the derivation of this species in continental Southeast Asia from P. waandersi or a waandersi-like ancestral form.Some aspects of the geohistory of the Indochinese Peninsula are dis-cussed from a zoogeographical viewpoint.
