118 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 56. 



21 millimeters; the eighth, 23 millimeters; the ninth, 18 millimeters; 

 the tenth, 13 millimeters; the eleventh, 15 millimeters. 



The sulci defining the dermal scutes are shallowly impressed, but 

 all except the posterior part of the costomarginal sulcus can be clearly 

 traced, as shown in figure 1. 



The vertebrals, as in all other known Belly River (Judith River) 

 Baenids, are wider than long. The principal dimensions of these as 

 compa,red with the type are shown in the table: 



Measurements of vertebrals of Ba'ena antiqua, in millimeters. 



There are four costal scutes on each side. These extend well 

 down on the shell, the costomarginal sulcus along the side, appar- 

 ently running with the costoperipheral suture, the center though 

 below it in front and apparently also behind. 



No supernumerary costal scutes are present. The nuchal is 

 rectangular in shape, 15 millimeters wide and 9 millimeters long. 



The plastron lacks the anterior end and can not, therefore, be 

 compared with the typical specimen, which consists only of the 

 anterior lobe. The posterior lobe has a length of 64 millimeters; 

 a width at the base of 72 milhmeters. Posteriorly from the inguinal 

 notch the lateral borders of the lobe, which are straight, gradually 

 converge to the truncated posterior end that measures 36 millimeters 

 in width. This end terminates 36 millimeters anterior to the median 

 posterior end of the carapace. The shallow concave surface of the 

 plastron suggests that this individual may have been a male. Be- 

 hind the inguinal notch the plastron has a thickness of 10 miUimeters, 

 but at the posterior extremity it reduces to only 3 milhmeters. At 

 the center the plastron has an extreme width of 134 millimeters; 

 the bridge a width of about 91 millimeters. There are well-devel- 

 oped mesoplastrals that meet on the median fine for 17 millimeters. 

 The lateral ends expand to a width of about 35 millimeters. The 

 hypoplastrals join along the median line for a distance of 55 milli- 

 meters; the xiphiplastrals for 31 millimeters. 



The abdominals meet on the median line for 28 millimeters; 

 femorals for 42 milhmeters; anals for 34 millimeters. There are four 

 inframarginal scutes on each bridge; these lie almost entirely on the 

 plastral bones. 



