Figure 1. The Cuatro Ciénegas valley in northeastern Mexico and the collecting sites of the three snail species and the cichlid from spring-fed habitats in the valley.

These pools and streams are arrayed around a mountain (Sierra de San Marcos) that juts into the center of the valley. Three geographic drainages are presented and color coded: western, Río Mesquites, and southeastern. Small black circles represent unsampled pools in the area. The valley is depicted as inset to the image on the right of the map that shows the boundary between Mexico and the United States.