56 FOSSIL TURTLES OF NORTH AMERICA. 



hinder end of the carapace has, at the time of burial, been crusht down to the plastron. After 

 having been weathered out of the matrix the specimen suffered further damage, all that part 

 behind the seventh neural having been destroyed. All the peripherals are likewise missing. 

 The length of the carapace (fig. 33) was originally about 120 mm.; the width was about 

 no mm. The shell is deprest and was so probably during life. The surface of the carapace 

 presents indistinct evidences of having been sculptured finely as in G. plicatulus, or possibly 

 more like Compsemys victa. The anterior border of the nuchal bone is eroded away. The 

 width of the bone was close to 38 mm. Its form is quite different from that of G. plicatulus. 

 In the latter the postero-lateral borders are nearly parallel with each other, while in the present 

 species they make nearly a right angle. The accompanying table presents the dimensions 

 of the neurals present. 



The great relative width of these neurals as compared with those of G. plicatulus is striking. 



The proximal end of the first costal is 14 mm. wide, while 

 the width at the middle of the length is 26 mm. In G. plicatulus 

 the median width is little more than the proximal. The succeed- 

 ing costals, at the middle of the length, measure as follows: 

 The second, 14 mm., the third, 14 mm., the fourth, 12 mm., 

 the fifth, 11.5 mm., the sixth, 19 mm. The third expands 

 distally to nearly 20 mm. The width of the sixth is relatively 

 much greater than that of G. plicatulus, but it corresponds to 

 the increased length of the sixth neural. 



The anterior lobe of the plastron appears to have been 

 rounded like that of G. plicatulus. The epiplastra are badly 



eroded, but the width of each is 13 mm. The entoplastron is 22 mm. long and 26 mm. wide. 

 The antero-lateral borders come together to form an obtuse angle; the hinder end of the 

 bone is more pointed. The mesoplastra are relatively broader fore and aft than those of G. 

 plicatulus. That of the right side is about 15 mm. wide at the midline; but it expands later- 

 ally, so that at the middle of its length the width is 24 mm. That of the left side is 23 mm. 

 wide at the midline, but narrows laterally for a short distance. The remainder is missing. It is 

 remarkable how close the hinder border of the mesoplastron comes to the inguinal buttress, 

 differing in this respect much from G. plicatulus. 



There are evidences of rather strong axillary and inguinal buttresses. They appear to 

 have articulated with the distal ends of the fifth and sixth costals, at their junctions. 



On account of the weathering to which this shell has been exposed, the boundaries of the 

 scutes can not be determined. 



Family BAENID.E Cope. 



Amphichelydia having the plastron firmly joined to the carapace by sutural union with the 

 lateral peripherals and with the costals by strongly developt axillary and inguinal buttresses. 

 Mesoplastra usually meeting at the midline and expanding toward the outer ends. Skulls, so 

 far as known, broad and short. Temporal roof extensive. Neck short, most of the vertebral 

 centra with only one end concave. 



To this family are assigned provisionally the genera Polythorax Cope and Archceochelys 

 Lydekker. The former possest intergular and interhumeral scutes; the latter genus appears to 

 have had a complete series of median plastral scutes. 



The BaeniJa; are closely related to the Pleurosternidte, but the great advances made in the 

 structure of the cervical vertebrae and the extension of the plastral buttresses seem to set the 

 species off as a distinct family. 



According to our present knowledge this family had an existence extending from the 

 Upper Jurassic to the Upper Eocene. Probaena, a close relative of Platychelys, of the Upper 

 Jurassic of Europe, has been described from the Como, or Morrison beds, occurring there with 

 Glyptops. Species belonging to Baena are now known from the Judith River beds, the Lara- 

 mie, and from all the divisions of the Eocene to the Uinta. Boremys Lambe comes from the 

 Judith River deposits, Eubaena from the Laramie, and Chisternon from the Bridger. 



Baena appears to be the genus most prolific of species and in most respects the one most 

 advanct. The carapace possesses a series of 8 neurals and a corresponding number of costals, 



