4 o 4 



FOSSIL TURTLES OF NORTH AMERICA. 



the third, which is nearly square, and the fifth, which is rhomboidal. The table gives the great- 

 est length and width of each neural. 



The costal plates have undergone considerable differentiation in form. The second, 

 fourth, sixth, and eighth have narrow proximal ends and wide distal ends; while the third 



and fifth have wide proximal and narrow distal ends. The 

 third comes into contact with 3 neurals, the fifth with only 2. 

 It is not unlikely, however, that other individuals will present 

 variations in the forms of the neurals and costals. 



The free borders of the plastron (plate 67, fig. 2; text-fig. 510) 

 are acute. The dimensions of the lobes are given in the table of 

 measurements. The anterior lip projects beyond the front of the 

 carapace about 50 mm. The base is 87 mm. wide from the 

 crossings of the gular sulci over the free border. The length of 

 the lip is 43 mm. The sides converge somewhat, and the rounded 

 anterior border is furnisht with 6 blunt teeth. The upper surface 



of the lip is convex, and it rises backward until the thickness becomes 33 mm. The hinder 

 face of this thickening is somewhat excavated. The entoplastron is pointed in front, broad 

 and somewhat rounded behind. 



The posterior lobe ends behind in 2 broadly rounded apices, which inclose a deep and 

 sharp notch. The borders of the apices are tootht. Just behind the inguinal notch the border 

 of the hypoplastron forms a wall about 25 mm. high. From the summit of this there is a slope 

 to the free edge. 



The sulci of the carapace are narrow grooves with raised edges. The nuchal scute has a 

 width of 28 mm. behind, but it is narrower in front. The sulci on the bridges are directed 



downward and forward. The vertebral scutes have considerably 



less lateral extent than do the costals. The accompanying table 

 presents in millimeters the greatest length and width of the 

 vertebrals. 



The gular scutes encroach on the entoplastron. The humeral 

 scutes meet along the midline for 76 mm.; the pectorals, 56 mm.; 

 the abdominal, 1 18 mm.; the femoral, 52 mm.; the anal, 36 mm. 

 Of the other parts of the skeleton there are present the 

 humerus, the pelvis, both femora, and the right tibia. The 

 humerus (fig. 511) lacks the distal end. It was bent more strongly than that of Gopherus 

 polyphemus, and the tuberosities are more strongly developt. The pelvis is represented by 

 figs. 512 and 513. The ischial tuberosities are pointed, and their apices are 45 mm. apart. 

 The extremity of the lateral and anterior pubic processes are missing. The ilium has the 

 proximal end much broadened antero-posteriorly, it being about 44 mm. The femur (figs. 

 514, 515) is unusually straight. The digital fossa is rather deep. 



In the Marsh collection at Yale University there is a large specimen which is to be referred 

 to this species. It was collected for Professor Marsh by Mr. J. B. Hatcher in the year 1889, 

 in the Titanotherium beds of South Dakota. It is at present designated by the receipt numbers 

 " 2054, box i ." The specimen was flattened somewhat during fossilization, but it was probably 

 originally of deprest form. Most of the hinder peripherals are now missing, as is also the 

 plastral lip. The second neural of this individual is octagonal, but the sides which are in 

 contact with the first and third costals of each side are very short. The third neural is approx- 

 imately square. All the others are hexagonal. The two suprapygals are about as in the type. 



The costal plates are strongly modified, having their proximal 

 ends alternately narrow and wide, while the distal ends are 

 alternately wide and narrow. Their dimensions are presented 

 in the table herewith. 



The first peripheral has an extent, backward from the free 

 edge, of 50 mm. The bridge peripherals rise a distance of 88 

 mm. above the carina which joins the free border of the third 

 peripheral with that of the seventh. On some of the free periph- 

 erals there is found a mucro, as in the type specimen. 



