Siebenrock's synopsis of living trionychids was based entirely on plastral characters.
Variation and relative growth in the plastral scutes of the turtle Kinosternon integrum LeConte.
The pattern of sculpturing on the plastral bones as well as that of the carapace is generally of anastamosing ridges.
The external scutellation of the plastral hinge in adults also differs from that in juveniles.
The gular scutes, on the anterior edge of the forelobe, become worn long before other plastral laminae do.
The smallest female, from Lajitas, having a plastral length of 6.9 centimeters, has a mottled carapace.