TAB. XIX C. 



Trionyx planus. 



Fig. 



1 . Upper view of the hind part of the carapace, half the nat. size. 



2. Inside view of the same specimen ; ph — -pfa, the fifth to the eighth costal plates 



inclusive. 



3. Peripheral border of the fifth costal plate, nat. size. 



4. Peripheral border of the fifth costal plate of the Trionyx Barbara, showing the 



difference in their relative thickness. 



