78 



FOSSIL TURTLES OF NORTH AMERICA. 



by the ribs of the vertebra mentioned. These buttresses extend inward from the sides of the 

 shell, forming partitions whose inner borders are distant from each other 85 mm. The upper 

 ends of the inguinal buttresses rise high against the contiguous borders of the fifth and sixth 

 costal plates. Between the axillary and the inguinal buttresses of each side there is a deep 

 sternal chamber. 



The anterior lobe is 70 mm. long, 90 mm. wide at the base, and 64 mm. at the gulo-humeral 

 sulci. It contracts gradually to these sulci, then sweeps round to the midline. The free 

 border is obtuse and the greater part of the lobe is 10 mm. thick. The entoplastron is long and 

 narrow, its length being 45 mm., its width 26 mm. The mesoplastra fail by about 16 mm. of 

 reaching the midline. Laterally they expand to a width of 64 mm. The bridges are 116 mm. 

 wide 62 per cent, of the length of that part of the plastron behind the axillary notches. 



The hinder lobe is 78 mm. long, 1 14 mm. wide at the base, and 80 mm. at the femoro-anal 

 sulci. The hinder border is slightly notcht. The free borders are subacute. At the inguinal 

 notch the thickness of the bone is 18 mm., but backward it thins to about 4 mm. 



The intergulars and the gulars both overlap the entoplastron. On each bridge there are 

 3 inframarginals, an axillary, another at the end of the pectoro-abdominal sulcus, and an 

 inguinal. The pectoral scute comes into contact with the sixth marginal. 



62. 



FlGS. 6166. Baena riparia. Type 



61. Scapula. 



62. Coracoid. 



63. Humerus, dorsal view. 



64. Humerus, radial border. 



65. Femur, dorsal view. 



66. Right hind leg. 

 66^3. Femur. 



The skull (plate 19, figs. I, 2) of this specimen is considerably 

 damaged. Most of the temporal roof is missing, as are the squa- 

 mosals and the premaxill.ne. The length from the latter bones to 

 the occipital condyle was close to 57 mm.; the breadth across the 

 quadrates is 56 mm. The orbit has a perpendicular diameter of 17 

 mm., a horizontal diameter of 15 mm., being somewhat larger than the orbit of B. sima, which 

 had a larger skull. The interorbital space is 18.5 mm. wide. The nasal opening is 17 mm. 

 wide. The narrowest part of the pterygoids is 13 mm. wide. On the inner border of the tritu- 

 rating surface of each maxilla there is a sharp ridge, as in B. sima. 



The lower jaw (plate 19, fig. 3) of this species differs greatly from that of B. sima, being of 

 much lighter construction and having a shorter symphysis. The distance from the tip of the jaw 

 to the middle of a line joining the front of one articulatory surface for the quadrate with that 

 of the other is 40 mm., the same as in the type of B. sima. The distance from the outside of one 

 of the articulatory surfaces to the other is 50 mm., much less than in B. sima. The height 

 of the middle of a ramus is 10 mm., the thickness 7 mm., the width of the gutter-like triturating 

 surface 4 mm. The length of the lower side of the symphysis is 15 mm. Of the sutures of the 

 upper surface of the skull the median, running between the nasals, prefrontals, frontals, and 

 parietals, and the transverse which separates the parietals from the frontals, are determinable. 



