Pick up your turtle very carefully so as not to frighten or drop it. Look at the tail and plastron - the bottom shell. If the shell is slightly concave it is usually a male. Male turtles' tails are also a bit longer and slightly wider at the base than a female. A female plastron will be flat or slightly convex. Sometimes a turtle's claws wil indicate gender. Males may have longer claws than females. In some species, adult females are larger than the males.