originally there were thought to be nine species, but this was reduced down to just 3 species. a fourth species was later discovered. the four currently known species of "endothiodon" are "e. bathystoma", "e. uniseries", "e. whaitsi", and "e. mahalanobsi". however, the basic distinction among the four species is size, which leads some to believe that "e. uniseries", "e. bathystoma", and "e. whaitsi" may actually represent an ontogenetic series rather than three distinct taxa. "e. mahalanobsi", on the other hand, is most likely a separate, truly smaller species based on the size of both juvenile and adult forms that have been found. apart from size, "e. mahalanobsi" also has a single longitudinal ridge on the snout (compared to three on the other species), a lower position of the pineal boss, and a swollen prefrontal bone.