TAB. XIXB. 



Fig. 



1 . Upper surface of the third costal plate, right side, of the Trionyx circumsulcatus, 



nat. size. 



2. Articular margin of ditto ; showing the natural curve and thickness of the plate. 



3. Peripheral margin of ditto ; showing the groove. 



4. Upper surface of the third costal plate, right side, of the Trionyx marginatum. 



5. Sutural margin of ditto. 



6. Peripheral margin of ditto. 



7. Upper surface of a fragment of a costal plate of the Trionyx pustulatus, nat. size. 



8. Under surface of ditto, showing the large and prominent adherent rib. 



9. Peripheral margin of ditto. 



