The genus Cualac is known from San Luis Potosi in the central part of Mexico. The genus is monotypic with Cualac tessellatus as the type species.

Cyprinodon, Cualac and Megupsilon form a clade.

Miller, R.R. 1956. A new genus and species of Cyprinodontid fish from San Luis Potosi, Mexico, with remarks on the subfamily Cyprinodontidae, Occasional Papers of the Museum of Zoology of the University of Michigan 581: 9-16, plate 1, figures 1-2.