2 7 8 



FOSSIL TURTLES OF NORTH AMERICA. 



1 60 mm. On the anterior portion of the carapace there is no median carina, but one of some 

 prominence begins on the sixth neural and continues to the end of the shell. Just above the 

 pygal plate this carina swells out into a considerable protuberance. The margin of the car- 

 apace is nowhere reverted, except slightly so behind the posterior legs. There is a slight 

 notch in the shell just over the tail. Whether or not the edges of the rear of the carapace were 

 to any degree serrated can not be determined with certainty, but they probably were not. 

 Anteriorly the edge of the shell is smooth ; over the neck the carapace somewhat exca- 

 vated; the plastron relatively small. The lobes, especially the hinder, leave large spaces 

 between the upper and lower parts of the shell. The bridge is narrow antero-posteriorly. 



The shell is rather thin in the dorsal and costal regions, from 4 mm. to 6 mm., but thickens 

 toward the margin, the last peripheral being about 10 mm. thick. The surface of the carapace 

 is usually smooth. 



In the middle line of the carapace we find, behind the nuchal, 8 neural plates and 2 supra- 

 pygals and the pygal. The first neural is of elongated oval form. The others, from the second 

 to the sixth, inclusive, are elongated hexagonal, with the broad end in front. The following 

 table gives the dimensions of the nuchal, the neurals, the two suprapygals and the pygal. 

 There are added the dimensions of B. wyomingensis, reduced to millimeters, from Leidy. 



The peripherals are high, the 

 first being 55 mm.; the fourth, 62 

 mm.; the tenth, at least 72 mm. 



The plastron (plate 42, fig. 2; 

 text-fig. 351) is the most interesting 

 and instructive portion of the shell. 

 Since all but a mere fragment of it 

 is peeled off the matrix, we must 

 depend on the impressions left on 

 the rock. As to the general form and 

 most of the sutures, there can be no 

 doubt. Its length was 282 



was 282 mm. 



The anterior lobe was 100 mm. 

 long, 138 mm. wide; the posterior 

 lobe 79 mm. long, 112 mm. wide at 

 the base. No trace is found of the 

 hyohypoplastral suture; 212 mm. 

 behind the front end of the plastron 

 is seen the very plain impression of the hypoxiphiplastral suture. It runs outward to near 

 the border of the plastron, then outward and forward, and finally turns abruptly backward to 

 the border. We must, however, remember that we are viewing the upper surface of the plastron, 

 and that these angulations represent processes of the bones. The xiphiplastrals had a length 

 of 72 mm. and a width of 100 mm. in front. 



There are very distinct impressions of the suture of the entoplastron and of the epiplastra. 

 The former was, on its upper surface, approximately circular, with a median lobe in front and 

 a narrow prolongation behind. Its length was 75 mm., the width, 55 mm. The hypoplastra 

 have a length of 45 mm. along the midline. 



The sulci are broad, but often extremely obscure; especially those which separate the 

 vertebral scutes from the costals. The marginal sulci are usually sufficiently distinct. The 

 transverse sulci of the vertebrals may be made out satisfactorily. As to the width of the ver- 

 tebrals, the drawing indicates the position of the lateral sulci as well as the faint indications 

 will permit. The marginal scutes did not rise on the sides as high as the peripheral bones. 

 There appear to have been axillary and inguinal scutes. In B. wyomingensis there is a com- 

 plete row of inframarginals. 



This species differs in various particulars from B. wyomingensis. Some differences appear 

 in the hinder neurals. There are in B. fluviatilis two suprapygals; in B. wyomingensis, 

 three. It will be observed from the measurements that the hindermost suprapygal is nearly 

 three times as wide as that of B. wyomingensis. There are obvious differences in the plastra, 

 that of the present species being more pointed behind. 



