Black-Knobbed Sawback Turtle Subspecies
A:Pattern on lower shell along scute seams mostly, usually covering less than 1/3 of the total surface area. Found in the Mobile and Tensaw river drainage of Alabama and Mississippi, including the Alabama River and its tributaries, but not found in the Mobile and Tensaw rivers themselves.
Northern Black-Knobbed Sawback Turtle, Graptemys nigrinoda nigrinoda
B:Intricate pattern on lower shell, usually covering most of the total surface area. Found only in the Mobile and Tensaw rivers of southern Alabama.
Southern Black-Knobbed Sawback Turtle, Graptemys nigrinoda denticola