This is a medium to large sized Minnesota turtle that grows 6 to 10 inches carapace length. The shell is dark brown, olive, or black. This turtle gets its name from the light yellow lines that form a reticulated or map like pattern on the back, but this pattern is usually obscure on adults.
Old females have dark blotches on the back and plastron.
There is a vertebral keel on the back that is rather prominent even in adults. The marginals on the rear of the carapace are serrated. The plastron is dull yellow with black lines and swirls. The head and limbs are black or dark olive. There are light yellow lines on the head and limbs.