Not much on them, they are the only mainly aquatic box turtle and are from Mexico, here is a cut and paste bit of info,
Coahuilan Box Turtles Terrapene coahuila
Only one race has been described for this species. It was formerly extremely rare in captivity, but in recent years, captive breeding has increased its availability to individuals. Coahuilan box turtles are the most aquatic members of the genus, and adults may attain lengths up to 6 inches (16cm). The carapace is usually horn colored and basically unmarked. Hind feet bear four toes and are webbed. T. coahuila are found only in the Cuatro Ciengas series of streams and water bodies in north eastern Mexico.