Artificial Key to North American Species and Subspecies of the Genus Trionyx
1. Septal ridges present; tubercles on anterior edge of carapace present or absent
2
Septal ridges absent; anterior edge of carapace lacking tubercles or raised prominences
19
2. Plastral area a uniform dark slate or blackish; soft parts of body blackish having large pale marks dorsally; carapace having large black blotches, often fused along margin, on pale background, and many well-defined longitudinal ridges
T. ferox, [p. 479]
Combination of characters not as above; ventral surface whitish, blackish flecks or blotches sometimes present
3