PLATE I. 



Fi". 1. Trionyx foveatus, Leidy, upper surface of the carapace shown in figure 1, p. 34; one-half the 

 natural size. Page 33. 



Fig. 2. Trionyx foveatus, lower or outer surface of a right hypoplastral bone ; natural size. Page 35. 



Fig. 3. Trionyx vagans, Cope, upper surface of carapace shown on page 37, figure 3 ; slightly less than 

 one-fourth natural size. Page 36. 



Fi". \. Portion of the upper surface of the same carapace, natural size ; to show the sculpture. 



