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The present specimens have carapace lengths of 250 and 238 mm. and plastral lengths of 185 and 176 mm.

Chelydra serpentina, which may occur sympatrically with C. rossignoni in some parts of Central America, has a narrower plastral bridge and only two barbels beneath the chin.

It was necessary to express plastral length as the sum of the lengths of forelobe and hind lobe.

Increment in plastral length for the first season of growth was expressed as a percentage of original plastral length because of variability of growth in the season of hatching; growth increments in the season following hatching are, therefore, not so great as indicated in Figure 11.

The gular scutes, on the anterior edge of the forelobe, become worn long before other plastral laminae do.