The submergence times of the diamondback water snake (Natrix rhombifera) and black rat snake (Elaphe obsoleta) were compared. Both species could easily survive underwater for periods greater than one hour. Furthermore, there was no difference in time of underwater survival in the two species. Some physiological and morphological parameters which may contribute to the ability of N. rhombifera and E. obsoleta to remain submerged were also examined. E. obsoleta was found to have a greater lung volume and larger and more numerous alveoli than N. rhombifera. Both species demonstrated a bradycardia upon submergence but it was less pronounced than the bradycardia of the true diving animals. It is concluded that N. rhombifera has few physiological adaptations for diving and that some of the physiological attributes for an aquatic existence have already developed in E. obsoleta
