The ringed map turtle or ringed sawback (Graptemys oculifera) is a species of turtle in the family Emydidae endemic to the southern United States. Male turtles may attain a carapace length of 10 cm (4 in). Females are larger, and may attain a carapace length of 22 cm (8.5 in). On the carapace are light-colored rings, which are thicker than the rings on Graptemys nigrinoda. It is frequently found in the Pearl River system in Louisiana and Mississippi. It shares this range with the Pearl River map turtle (G. pearlensis). Graptemys is a genus of freshwater turtles containing 14 species, commonly known as map turtles. Graptemys are small to medium-sized turtles that are sexually dimorphic, with females attaining as much as twice the length and ten times the mass as males in some species. Depending on the species, adult males range from 7–16 cm (2.75–6.25 in), adult females 10–29.5 cm (4–11.62 in), and hatchlings 2.5–3.8 cm (1–1.5 in). although some sources indicate female Barbour's map turtles (Graptemys barbouri) grow to 33 cm (13 in) in length. Most species have a distinctive dark pigmented keel that is often notched or serrated running down the center of the carapace and serrated scutes on the rear margin. The head, neck, and limbs exhibit bold patterns of yellow (occasionally orange or red) lines and spots against darker green, olive, or black base colors. The patterns on the head can be important characters in identifying the various species. The common name "map turtle" is derived from the intricate patterns on their shells that are suggestive of topographical maps, although the patterns are more apparent in some species than others, and often become obscure in older specimens. Some species are occasionally called "sawbacks", in reference to the serrated keels on their shell. They are endemic to North America, where most species occur in the rivers of the Gulf Coast of the United States, although three species are more wide-ranging, dispersed throughout the eastern two thirds of the greater Mississippi River basin, into the Great Lakes region, and east to New York and southeast Canada. Most Graptemys are lotic, river turtles, having a preference for moving water and larger lakes, and with long legs, broad feet, and long fully webbed digits they are well adapted for swimming in currents.