male elasmobranchs (sharks and rays) have what are called "claspers". They are a finger like appendage that protrudes from the caudal fins and are used to grasp the females during mating. Males have junk and the females do not.
You can tell the sex of Sharks and Rays the same way. The picture below shows you. If you look at the picture of the Ray above, you can see his claspers.