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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.

The mathematical mean of the ratio, abdominal length/plastral length, in each of the four groups of larger-sized turtles, was not significantly different from the same ratio in the hatchling group.

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

Increments in plastral length averaged 68.1 per cent in the year after hatching, 28.6 per cent in the second year and 18.1 per cent in the third year.