EXPLANA'J'ION OF PLATE XV. 



Figs. 1-5. Ba^ na arenosa : 



Fig. 1. Anterior extremity of the i)lastron,'eshil)itiiig 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, from another specimen found by Dr. Carter on 



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



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

 Fi"'. 3. From a specimen fonud by Dr. Corson at Grizzly Buttes. It is of greater proportiou- 



ate breadth than the former, and presents x 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 "at the junction of Big Sandy ^nd 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 th3 eutosternal bone. 



Fi"-. 6. Baptemvs wyomingensis. One-half the natural size. A portion of the anterior extremity of 

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

 presents no distinction between gular and humeral scute areas. 



Fig. 7. Tbstudo CoRSONi. Anteriorextremityof a plastron, one-half the natural size. From a specimen 

 discovered by Dr. Corson at Grizzly Buttes. 



Fio-, 8. Supposed turtle egg, natural size. A frequent fossil of the indurated clays of the Bridgcr bf'ds. 

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

 also fonud, like that represented in Fig. 01, Plate XXXII. They have an outer calcareous 

 crust, and are iilled with the same material as the imhe<ldiug matrix. Usually one end is 

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

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

 Figs. 60, 61, Plate XXXII. 



Fi'^ 9. Hybemys arenakius. A marginal plate, exhibiting the bosses ou its outer extension. From 

 a specimen found by Prt)fes8or Haydeu's party on Little Sandy Creek. Natural size. 



Fig. 10. Stylemys OREGONEN.SI8. A vertebral plate, one-half the natural size. From Crooked River, 

 Oregon. 



Figs. 11-13. NoTHOSAUKOPS OCCLDUUS. Three views of a vertebra, natural size, from .i specimen ob- 

 tained by Professor Haydeu on Moreau River. 

 Fig. II. 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, ou Dry Creek, Wyoming. 

 Fig. 15. Saniwa ensiden.s. Two dorsal vertebrai as they lie iu the matrix, inferior view, 

 from a specimen obtained near Granger, Wyoming, during Professor Haydeu's exploration. 



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

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

 Colorado. 



Fjo-. 16. End view, exhibiting the articular surface of the centrum. 



Fig. 17. Side view. 



Fig. 18. View of the Ijroken surface of the vertebra, exhibiting the large areola^ of the 

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



