Q6 FOSSIL TURTLES OF NORTH AMERICA. 



its antero-posterior extent was only about 30 mm. Were the anterior excavation not present, 

 the fore-and-aft extent of the nuchal would be about normal. 



The first peripheral has a fore-and-aft extent of about 43 mm. Its length, parallel with the 

 border, can not be accurately determined; it was about 65 mm. From this specimen it can not 

 be learned where the sutures between the costal and the peripheral bones were situated, except 

 in the case of the first peripherals. However, since in both Glxptops and Ba'ena these sutures, 

 over the bridges, follow the sulci between the costal and marginal scutes, it is probable that 

 they do so in Thescelus. In Glyptops plicatulus, behind the bridges, the sutures rise a 

 considerable distance above the epidermal sulci; in Ba'ena emilice, a very little above. In 

 Thescelus insiliens the structure of the surface of the bone appears to indicate that behind the 

 bridges the sutures are placed somewhat above the scutal sulci, and they are accordingly so 

 represented provisionally. 



The number and the extent of the peripherals along the border can not be made out with 

 certainty. 



The epidermal scutes and their limits are for the most part determinable. The sulci are 

 narrow and shallow, but usually distinct. The first vertebral is 60 mm. long in the midline, 

 concave in front, behind, and on each side. The width behind is 75 mm., but in front it is 

 expanded to 98 mm. The next three vertebrals are from 90 mm. to 95 mm. wide. The exact 

 limit between the fourth and the fifth can not be determined. The fifth vertebral is 1 iomm.wide. 



There seems to have been no nuchal scute. The first marginal on each side is very narrow, 

 8 mm. to 10 mm., and extends along the free border of the carapace 30 mm. The succeeding 

 marginals increase in height and length to the fourth, which is 55 mm. high and occupies 

 85 mm. of the free border. The succeeding marginals retain this width to beyond the inguinal 

 notch; the posterior are much narrower. There were probably paired supracaudal scutes. 



The plastron (plate 25) has a median length of 420 mm. The anterior lobe has a length of 

 117 mm. The base is 170 mm. wide, but the lobe narrows forward so rapidly that at the 

 crossings of the gular sulci the width is only 91 mm. The posterior lobe is 1 10 mm. long, 

 168 mm. wide at the base, and 130 mm. wide at the ends of the femoro-anal sulci. The 

 posterior end is broad, and occupied by a wide emargination 10 mm. deep. 



The bridge is 194 mm. wide, fore and aft. From its inner end to the border of the carapace 

 is about 120 mm. 



The sutures bounding the epiplastron and the entoplastron are not demonstrable; hence 

 they are represented provisionally. The thickness of the epiplastra is about 9 mm. 



There are very broad mesoplastra extending across the plastron. The width of the outer 

 end of each bone is about 100 mm., being apparently a little greater on one side than on the 

 other. Where the bones meet at the midline they are 54 mm. wide. These mesoplastra differ 

 from those of Glyptops in being proportionally larger and in having their median ends narrower 

 than the outer. They are much like those of Ba'ena emilice. 



The extent of the hyoplastra along the midline equals about 105 mm.; that of the hypo- 

 plasia 100 mm. The anterior borders of the xiphiplastra run straight across the plastron, 

 except near the border of the plastron, where they send forward on each side an angular 

 process into the hypoplastron. Just behind this process the xiphiplastron is 10 mm. thick; 

 near the hinder end, 6 mm. 



The intergulars and gulars of this species are much like those of Bacna emilice. The 

 former, taken together, extend 30 mm. from side to side; 16 mm. fore and aft. The gulars are 

 very large, the sulci bounding them behind meeting the midline 54 mm. behind the front of 

 the plastron, and diverging with an angle of about 140 . If the entoplastron has been even 

 approximately defined, the humero-pectoral sulcus falls far behind it. The fore-and-aft 

 extent of the humerals along the midline is 87 mm. The sulci between the pectorals and the 

 abdominals are deflected backward near the midline on each side. The pectorals occupy- only 

 55 mm. of the midline. The femorals are 60 mm. fore and aft; the anals 72 mm. The femoro- 

 anal sulci are directed far forward as they approach the midline, exactly as in Bacna. 



On the bridge there are 4 large inframarginals whose boundaries have been satisfactorily 

 determined. 



The buttresses of the plastron are intermediate, in extent of development, between those of 

 Glyptops and Bacna. 



