The plastron of the male looks slightly concave while the female's is flat.
From the en.wikipedia.org
The male also has a plastron that is curved inwards to aid reproduction.
From the en.wikipedia.org
Sea turtles have a carapace and plastron of bone and cartilage which is developed from their ribs.
From the en.wikipedia.org
Another way is the plastron, which is concave in the male and flat or slightly convex in the female.
From the dispatch.com
The necks of the cows are embellished with a kind of plastron, some of the cows are depicted as wearing decorative robes.
From the en.wikipedia.org
Underneath, the turtle's plastron is hued yellow.
From the en.wikipedia.org
The clownfish plastron necklace, for instance, took 750 hours to produce and has a total of 2,160 individually set stones.
From the forbes.com
The top part of the shell is the carapace, the underside is the plastron, and the two are connected by the bridge.
From the en.wikipedia.org
The plastron of a female tortoise often has a noticeable V-shaped notch below the tail which facilitates passing the eggs.
From the en.wikipedia.org
More examples
The ornamental front of a woman's bodice or shirt
The front of man's dress shirt
A metal breastplate that was worn under a coat of mail
A large pad worn by a fencer to protect the chest
(zoology) the part of a turtle's shell forming its underside
The plastron is the nearly flat part of the shell structure of a turtle or tortoise, what one would call the belly, similar in composition to the carapace; with an external layer of horny material divided into plates called scutes and an underlying layer of interlocking bones.
The shell covering the underside (bottom) of a turtle or other animal
An armor metal breastplate or the fur front of the sideless surcoat worn by medieval ladies.
The ventral part (bottom) of the shell of a turtle or tortoise shell