Five species of pupfish, genus Cyprinodon, are known from Laguna Chichancanab, an endorheic basin in the interior of the Yucatan Peninsula of Mexico. The 5th of these is described as C. verecundus sp. nov., is the rarest species in the lake. It differs from its sympatric congeners in its large fins, larger eye and low gill raker counts. Although it occurs with all 4 of the other pupfish it has not been collected at every locality and may be restricted to habitats with firm substrate. Multivariate analyses support the recognition of this species and offer evidence that it is not a hybrid between any species pair in the lake.