Thanks for you help, Dear Kelly, For most dolphin species, you cannot tell the difference between male and female dolphins if you see them in the wild. You can be sure a dolphin is a female if you see it closely accompanied by a calf. Dolphin fathers do not help to raise their young. In some species the males are slightly larger than the females, but there is so much individual variation in size that this is not a foolproof way to identify free swimming males and females. In order to determine the sex of dolphins, you must be able to see their bellies.
Females have a genital slit closer to the tail and have mammary slits on either side.
This design protects the dolphins' genitals and makes the animals more streamline for faster swimming.