EXPLANATION OF PLATE XXX. 



Figs. 1-4. Tjesttjdo Corsoni : 



Fig. 1. Intermediate portion of the carapace, one-half the natural size, exhibiting the series 

 of vertebral plates, from the first to the eighth and part of the ninth, and contiguous por- 

 tions of the costal plates. Specimen discovered by Dr. Joseph K. Corson on the buttes of 

 Dry Creek, and presented by him to the Academy of Philadelphia. 



Fig. 2. Plastron, or lower shield, one-third the natural size. Specimen discovered by Dr. 

 Corson on Grizzly Buttes, and presented to the Academy. 



Fig. 3. Anterior process of another plastron, one-half the natural size. From a specimen 

 discovered by Dr. Corson in the same locality as the last. 



Fig. 4. Anterior process of a nearly complete plastron, one-half the natural size. From a 

 specimen discovered by Mrs. Dr. Carter on the buttes of Dry Creek, and presented by her 

 to the Academy of Philadelphia. 



Fig. 5. Cladocyclus occidentaiis : 



Large scale, imbedded in a lead-colored calcareous shale, natural size. Specimen obtained 

 by Professor Hayden from the Cretaceous formation of Sage Creek, Dakota. 



