EXPLANATION OF PLATE XIII. 



Babna arenosa : 



Figures one-half the natural size. 



Figs. 1, 2. Specimen on which the genus and species were originally established. Dis- 

 covered at the junction of the Big Sandy and Green Rivers, Wyoming, during Professor 

 Hayden's exploration of 1870. 



Fig. 1. View of the carapace. 



Fig. 2. View of the plastron, its anterior extremity lost. 



Fig. 3. View of the plastron of another specimen, originally referred to a species with the 

 name of Baena affinis. It was discovered by Dr. Carter at Church Buttes, and was pre- 

 sented by him to the Academy of Natural Sciences of Philadelphia. 



