EXPLANATION OF PLATE XV. 



Figs. 1-5. Baena arenosa: 



Fig. 1. Anterior extremity of the plastron, exhibiting the two pairs of gular scute areas. 



From the same specimen as Fig. 3, of Plate XIII. One-half the natural size. 

 Fig. 2. Anterior extremity of the plastron, froih another specimen found hy Dr. Carter on 



Henry's Fork of Green River. Tho gular scute areas are larger, and the surface of the 



plates is comparatively smooth. One-half the natural size. 

 Fig. 3. From a specimen found hy Dr. Corson at Grizzly Buttes. It is of greater proportion- 

 ate breadth than the former, and presents a want of symmetry in the gular scute areas. 



One-half the natural size. 

 Figs. 4, 5. Of the natural size. From a young specimen obtained by Professor Haydeu's 



party aj; the junction of Big Sandy and Green Rivers. It retains the sutures, which are 



obliterated in the preceding mature specimens. 

 Fig. 4. Inferior view. 

 Fig. 5. Superior view, exhibiting the trident form of tha eutosternal hone. 



Fig. 6. Baptemys wyomingensis. One-half the natural size. A portion of the anterior extremity of 

 the plastron, from a specimen ohtained hy Professor Haydeu's party at Church Buttes. It 

 presents no distinction between gular and humeral scute areas. 



Fig. 7. Testudo Corsoni. Anterior extremity of a plastron, one-half the natural size. From a specimen' 

 discovered hy Dr. Corson at Grizzly Buttes. 



Fig. 8. Supposed turtle egg, natural size. A frequent fossil of the indurated clays of the Brklger beds. 

 They are usually ahout the size of the specimen represented, though quite small ones are 

 also found, like that represented in Fig. 61, Plate XXXII. They have an outer calcareous 

 crust, and are filled with the same material as the imbedding matrix. Usually one end is 

 truncated and rough, as if the shell had been originally broken. Sometimes the truncated 

 end appears covered with a low conical disk, resembling an operculum, as represented in 

 Figs. 60, 61, Plate XXXII. 



Fig. 9. Hybemys arenarius. A marginal plate, exhibiting tho bosses on its outer extension. From 

 a specimen found by Professor Haydeu's party on Little Sandy Creek. Natural size. 



Fig. 10. SIylemys oregonensis. A vertebral plate, one-half the natural size. From Crooked River, 

 Oregon. 



Figs. 11-13. Nothosaurops occiDTjus. Three views of a vertebra, natural size, from a specimen ob- 

 tained by Professor Hayden on Moreau River. 

 Fig. 11. Side view of the centrum, exhibiting the sutural surface of the neural arch. 

 Fig. 12. Upper view of the same. 

 Fig. 13. View of the anterior end. 



Figs! 14, 15. Saniwa. Natural size. 



Fig. 14. Saniwa major. Distal extremity of a humerus, from a specimen found by Dr. 



Carter at the Lodge-pole trail, on Dry Creek, Wyoming. 

 Fig. 15. Saniwa ensidens. Two dorsal vertebra? as they lie in the matrix, inferior view, 



from a specimen ohtained near Gra»ger, Wyoming, during Professor Hayden's exploration. 



Figs. 16-18. Antrodemus. In the text, page 267, under tho name of Poicilopleuron valens. Figures 

 one-half the natural size. Three views of one-half of a vertebra, from Middle Park, 

 Colorado. 



Fig. 16. End view, exhibiting the articular surface of the centrum. 



Fig. 17. Sido view. 



Fig. 18. View of the broken surface of the vertebra, exhibiting the large areola? of the 

 interior of the centrum, inclosed by thick walls of compact substance. 



